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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 11-12-2013, 07:08 AM
Arcite Arcite is offline
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Steady high-pitched electronic whine

I bought a 2011 335i xDrive sedan about 3 weeks ago. As I was driving it home, I noticed something I hadn't noticed on the test drive: a constant, extremely high-frequency electronic-sounding whine inside the cabin. It sounds like the noise you hear when you're in a room with an old CRT television that's powered on but not tuned to a channel. It "steps" up or down slightly in pitch when I apply or back off the throttle, but other than that, it's related strictly to road speed and not engine speed: it starts once I pass about 15 mph, and goes away when I slow to less than about 15 mph--literally, I can be coasting at 55 mph with the transmission in neutral and the engine idling, and the noise will be there.

Searching reveals many past threads on similar sounds, but some seem to have been mechanical in nature; it's hard to believe this one is, given the electronic sound of it and steady pitch. No one seems to have found a definitive answer. The closest thread I've found to describing what I'm hearing is this one. Some people there say it was related to a muffler flap vacuum actuator. Has anyone else here had this problem and gotten it solved? I'm taking the car to the dealership on Thursday (also has a slow engine coolant leak) and would like to have something to tell them.
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  #2  
Old 11-12-2013, 08:31 AM
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Quote:
Originally Posted by Arcite View Post
I bought a 2011 335i xDrive sedan about 3 weeks ago. As I was driving it home, I noticed something I hadn't noticed on the test drive: a constant, extremely high-frequency electronic-sounding whine inside the cabin. It sounds like the noise you hear when you're in a room with an old CRT television that's powered on but not tuned to a channel. It "steps" up or down slightly in pitch when I apply or back off the throttle, but other than that, it's related strictly to road speed and not engine speed: it starts once I pass about 15 mph, and goes away when I slow to less than about 15 mph--literally, I can be coasting at 55 mph with the transmission in neutral and the engine idling, and the noise will be there.

Sounds like a signal's being picked up by your audio system. Spectrum analysis, please.
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  #3  
Old 11-12-2013, 09:36 AM
fdriller9 fdriller9 is online now
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Yea I agree with Cal...sounds like noise is entering the system somewhere.

I would start at the amp in the trunk, driver's side. Check if there is water in there. It's a common issue and the water damage could be "minor" just cause noise to enter the system.
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  #4  
Old 11-13-2013, 03:43 PM
Arcite Arcite is offline
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Today I tried something. One of the people in one of the other threads, specifically in this post, said that he had the issue and posted a link to another thread describing a "mod" that fixed it. This "mod" involves nothing more than unplugging an actuator in the trunk. I tried this this morning, and lo and behold, the noise was gone. I'm not going to keep it unplugged, but at least now I have some information to take to the dealership.
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  #5  
Old 11-13-2013, 05:07 PM
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Quote:
Originally Posted by Arcite View Post
Today I tried something. One of the people in one of the other threads, specifically in this post, said that he had the issue and posted a link to another thread describing a "mod" that fixed it. This "mod" involves nothing more than unplugging an actuator in the trunk. I tried this this morning, and lo and behold, the noise was gone. I'm not going to keep it unplugged, but at least now I have some information to take to the dealership.

You mean the exhaust flap, driver's side? Plug in rear, trunk?
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  #6  
Old 11-13-2013, 06:26 PM
Arcite Arcite is offline
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Originally Posted by CALWATERBOY View Post
You mean the exhaust flap, driver's side? Plug in rear, trunk?
That's the one. Simply unplugged it, drove off, and the noise was not present.
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  #7  
Old 11-14-2013, 08:14 AM
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Originally Posted by Arcite View Post
That's the one. Simply unplugged it, drove off, and the noise was not present.
Replace the flap electrical portion. Broadcasting either back through wire or air. That ol' spectrum analyzer would tell the tale....
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  #8  
Old 11-14-2013, 03:08 PM
Arcite Arcite is offline
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I took it to the dealership today, and told them about unplugging the exhaust flap plug. The guy thought it was weird, and told me if I wanted to I could drive around with it unplugged, and that it wouldn't hurt anything. Later in the morning, he called me and said they had overnighted a part related to the problem, and it would be done tomorrow. So I guess they at least think they found a way to fix it. Which is good, because I actually didn't like the increased engine noise at low speeds with the flap open.
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  #9  
Old 11-15-2013, 02:27 PM
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Quote:
Originally Posted by Arcite View Post
I took it to the dealership today, and told them about unplugging the exhaust flap plug. The guy thought it was weird, and told me if I wanted to I could drive around with it unplugged, and that it wouldn't hurt anything. Later in the morning, he called me and said they had overnighted a part related to the problem, and it would be done tomorrow. So I guess they at least think they found a way to fix it. Which is good, because I actually didn't like the increased engine noise at low speeds with the flap open.

Yeah, ain't that melodious. Also, lack of back pressure lowers power @ lower rpm. Ug! Might feel better at first, but with experience you'll see.
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  #10  
Old 11-18-2013, 02:48 PM
Arcite Arcite is offline
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Well, I got my car back today. They said they replaced the flap actuator, but the noise is still there. I wasn't about to turn back around and demand they take it back, as I had to get to a work meeting, and it seems like such a petty little thing, but it really affects my enjoyment of the car. Any ideas? As I said, there are a bunch of threads about this, but half of them petered out without the OP mentioning having gotten rid of the noise, and the other half say they got it fixed but don't describe how.
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  #11  
Old 11-19-2013, 08:17 AM
BostonB6 BostonB6 is offline
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Quote:
Originally Posted by Arcite View Post
Well, I got my car back today. They said they replaced the flap actuator, but the noise is still there. I wasn't about to turn back around and demand they take it back, as I had to get to a work meeting, and it seems like such a petty little thing, but it really affects my enjoyment of the car. Any ideas? As I said, there are a bunch of threads about this, but half of them petered out without the OP mentioning having gotten rid of the noise, and the other half say they got it fixed but don't describe how.

Why not IM/PM those that had it sucessfully fixed for more info?
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  #12  
Old 11-22-2013, 06:56 AM
Arcite Arcite is offline
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Why not IM/PM those that had it sucessfully fixed for more info?
OK, I have started to do this.

In the meantime, CALWATERBOY, I had to google "spectrum analyzer." Very interesting, but I don't happen to have one lying around, and they seem to cost at least $1000. I'm curious, though, how could the information obtained by one be used to actually identify the problem?
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  #13  
Old 11-22-2013, 07:17 AM
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Quote:
Originally Posted by Arcite View Post
Well, I got my car back today. They said they replaced the flap actuator, but the noise is still there. I wasn't about to turn back around and demand they take it back, as I had to get to a work meeting, and it seems like such a petty little thing, but it really affects my enjoyment of the car. Any ideas? As I said, there are a bunch of threads about this, but half of them petered out without the OP mentioning having gotten rid of the noise, and the other half say they got it fixed but don't describe how.

Still goes away if unplugged?

Ask dealeer exactly how they troubleshot it; post detail here!

Then, complain that problem not fixed, a thing they should have realized before they released it to you. Which dealer?
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  #14  
Old 11-22-2013, 08:35 AM
Akleifg Akleifg is offline
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Could it be the turbo? Maybe the ground wire on the stereo is off? Does it rev up with the engine?
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Old 11-22-2013, 09:10 AM
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fun2drive fun2drive is offline
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High frequency noise feeding back can be solved with a high frequency filter if that is what is going on. Ever notice that black 3/8" by 1" black plastic thing on a lot of computer laptop power cords just before it enters the plug on the laptop? That is an electrical filter to stop RF feeding from 60Hz into your display or sound system. You say high frequency which to me is a couple thousand Hz. If this is low frequency like 60Hz a simple choke could solve the problem. What seems odd to me is that this problem started now.
It is very easy to install a choke on the wiring and see if that works. I have no idea what the dealer would do to solve this since I am sure they would never propose a solution like this. I can only assume that the line is picking up the solenoid that is running the flapper valve and feeding it back into your audio system. Weird...
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  #16  
Old 11-22-2013, 09:15 PM
Arcite Arcite is offline
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Originally Posted by CALWATERBOY View Post
Still goes away if unplugged?

Ask dealeer exactly how they troubleshot it; post detail here!

Then, complain that problem not fixed, a thing they should have realized before they released it to you. Which dealer?
Haven't tried unplugging it again yet, but I suspect my unplugging it may have thrown them off (even though I told them I had done so.) I've read in other threads that unplugging it causes an error code--they may have chased that error code down a rabbit hole, thinking that was the source of the problem. And it's Classic BMW in Willoughby Hills, OH, though I don't want to be too hard on them yet since they're not the ones who sold me the car. As I said upthread, I realized the noise was still there as I was speeding off to a work meeting I was about to be late to, so I wasn't about to spin around and go back.

Quote:
Originally Posted by Akleifg View Post
Could it be the turbo? Maybe the ground wire on the stereo is off? Does it rev up with the engine?
No, I can hear the turbo spool up independently; this sound is not related. As I said in the OP, it doesn't vary with engine speed--just comes in or cuts off at around 15-16 mph road speed, independent of engine speed/braking/throttle application or lack thereof/whatever.

Quote:
Originally Posted by fun2drive View Post
High frequency noise feeding back can be solved with a high frequency filter if that is what is going on. Ever notice that black 3/8" by 1" black plastic thing on a lot of computer laptop power cords just before it enters the plug on the laptop? That is an electrical filter to stop RF feeding from 60Hz into your display or sound system. You say high frequency which to me is a couple thousand Hz. If this is low frequency like 60Hz a simple choke could solve the problem. What seems odd to me is that this problem started now.
It is very easy to install a choke on the wiring and see if that works. I have no idea what the dealer would do to solve this since I am sure they would never propose a solution like this. I can only assume that the line is picking up the solenoid that is running the flapper valve and feeding it back into your audio system. Weird...
That's an interesting idea. BTW, the problem didn't just start now--as I said in the OP, I bought the car CPO last month, just didn't notice it till the day after I drove it home. For all I know, the noise was there the day the car rolled off the assembly line.

How would I know which line to install the choke on? The muffler flap actuator wiring?
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  #17  
Old 11-23-2013, 01:04 AM
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Originally Posted by Arcite View Post
Haven't tried unplugging it again yet, but I suspect my unplugging it may have thrown them off (even though I told them I had done so.) I've read in other threads that unplugging it causes an error code--they may have chased that error code down a rabbit hole, thinking that was the source of the problem. And it's Classic BMW in Willoughby Hills, OH, though I don't want to be too hard on them yet since they're not the ones who sold me the car. As I said upthread, I realized the noise was still there as I was speeding off to a work meeting I was about to be late to, so I wasn't about to spin around and go back.

Though SA's may come from the lower centiles, often populated with outpatients in CIA drug trials and supervised release programs, mechanics are a different breed, possessing expertise and experience.

None the less, rare is the BMW mech that is conversant in electronics. Dealer cannot be expected to track down spurious signals - you may be the best bet on that.
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Old 11-23-2013, 01:09 AM
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Originally Posted by fun2drive View Post
High frequency noise feeding back can be solved with a high frequency filter if that is what is going on. Ever notice that black 3/8" by 1" black plastic thing on a lot of computer laptop power cords just before it enters the plug on the laptop? That is an electrical filter to stop RF feeding from 60Hz into your display or sound system. You say high frequency which to me is a couple thousand Hz. If this is low frequency like 60Hz a simple choke could solve the problem. What seems odd to me is that this problem started now.
It is very easy to install a choke on the wiring and see if that works. I have no idea what the dealer would do to solve this since I am sure they would never propose a solution like this. I can only assume that the line is picking up the solenoid that is running the flapper valve and feeding it back into your audio system. Weird...
Yessir! Could be as easy as a ferrite clamped around the wires. Dunno what BMW's doing with the flap - simple DC on/off?
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Old 11-23-2013, 03:26 PM
Arcite Arcite is offline
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Can anyone suggest what kind of choke/filter to try? It definitely is a high-frequency noise, at least a couple thousand hertz... like I said, it sounds like the noise from a CRT TV. Extremely high-pitched, at the very upper range of human hearing.
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Old 11-23-2013, 09:01 PM
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Originally Posted by Arcite View Post
Can anyone suggest what kind of choke/filter to try? It definitely is a high-frequency noise, at least a couple thousand hertz... like I said, it sounds like the noise from a CRT TV. Extremely high-pitched, at the very upper range of human hearing.
An old laptop power supply might have a cylindrical thing under the insulation around the wires. Probable ferrite to zap exactly what you're looking to prevent. Try harvesting; clamp on your wires.
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Old 11-24-2013, 05:23 AM
fdriller9 fdriller9 is online now
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Having the error code in your dme doesn't harm anything. It's a shadow fault and no lights are tripped.

You can leave it unplugged and have a shadow fault stored in the dme.

Or you can get under the car and pull the vacuum line off the butterfly valve and plug it with a golf tee. Hence the "golf tee" mod. There will be no shadow fault. But this may not solve your issue.
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Old 11-24-2013, 08:59 AM
sbussard sbussard is offline
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This phenomena sounds like a power line too close to an amplifier or speaker wire causing feedback through the stereo. Not sure if the stereo system is still completely stock, but that is one thing in my old "boom-boom" days that you would see frequently with amature stereo installations. It's a little odd that it goes away when you disconnect the exhaust flap. See if you can trace the routing of the power wires for the flap. Make sure they are a minimum of 6" away from the amplifier, and any other type of sound signal wires going to the speakers. Good luck!
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Old 11-24-2013, 11:28 AM
Arcite Arcite is offline
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Originally Posted by CALWATERBOY View Post
An old laptop power supply might have a cylindrical thing under the insulation around the wires. Probable ferrite to zap exactly what you're looking to prevent. Try harvesting; clamp on your wires.
I have a few laptop power supplies lying around. Those things are molded into the cable, though. Not something you can just pry off and clamp onto something else.

Quote:
Originally Posted by fdriller9 View Post
Having the error code in your dme doesn't harm anything. It's a shadow fault and no lights are tripped.

You can leave it unplugged and have a shadow fault stored in the dme.

Or you can get under the car and pull the vacuum line off the butterfly valve and plug it with a golf tee. Hence the "golf tee" mod. There will be no shadow fault. But this may not solve your issue.
I know, but I don't like the louder exhaust sound with the flap always open.

Quote:
Originally Posted by sbussard View Post
This phenomena sounds like a power line too close to an amplifier or speaker wire causing feedback through the stereo. Not sure if the stereo system is still completely stock, but that is one thing in my old "boom-boom" days that you would see frequently with amature stereo installations. It's a little odd that it goes away when you disconnect the exhaust flap. See if you can trace the routing of the power wires for the flap. Make sure they are a minimum of 6" away from the amplifier, and any other type of sound signal wires going to the speakers. Good luck!
They definitely are close to the amplifier. Both are in compartments near the back of the trunk on the driver's side. However, if the noise was caused by feedback to the amplifier, would it still be there even when the sound system is off? Because it is.
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Old 11-24-2013, 11:46 AM
sbussard sbussard is offline
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Originally Posted by Arcite View Post
They definitely are close to the amplifier. Both are in compartments near the back of the trunk on the driver's side. However, if the noise was caused by feedback to the amplifier, would it still be there even when the sound system is off? Because it is.

That really depends. Do you have navigation, and or bluetooth? If you do, it will definately still make noise. With the navigation system, and or bluetooth, the speaker system is always active when the car is on, even if you aren't listening to music. Now, with that said, if the power lines are still routed the way they were from the factory, chances are slim this is the culprit. Even so, if they can be pulled away from the amp, and or speaker wires, it may be worth trying to give them a little more space, and see what happens. I would be surprised if it helps, assuming everything is "as it should be" from the factory, but what do you have to loose.

I believe it was also stated in an early reply to check all your grounds. It's unlikely you have a bad ground back at the battery, but a bad ground on the chassis, or on the engine can certainly cause some unpleasant feedback.
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Old 11-24-2013, 12:57 PM
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Quote:
Originally Posted by Arcite View Post
OK, I have started to do this.

In the meantime, CALWATERBOY, I had to google "spectrum analyzer." Very interesting, but I don't happen to have one lying around, and they seem to cost at least $1000. I'm curious, though, how could the information obtained by one be used to actually identify the problem?

Working in the frequency domain, you at least can see what freq is at issue, so maybe know where to look.

Also, can follow upstream to source if conducted EMI [ElectroMagnetic Interrference]. If radiated [broadcast], break out the horns & loop antennae.

All electrical devices for sale in the USA must meet FCC standards for Inductive, Capacitive, Radiative, and Conducted EMI. Vendors are required to self-certify and the whole automobile might be driven into an anechoic chamber [EMI isolated] for testing. Here's an example in Victoria, Australia:





Here's another kind of vehicle in for radar testing:


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