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Discussion Starter · #1 ·

This horrible noise started during a recent cold snap and has continued even after the weather warmed up above freezing. It occurs primarily when the engine is cold or warming up, under constant throttle. Noise goes away when I lift off the throttle. 2004 325ci, manual, 121000 miles. Anyone have an idea what is causing this? Thanks in advance!
 

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RayMondo
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This horrible noise started during a recent cold snap and has continued even after the weather warmed up above freezing. It occurs primarily when the engine is cold or warming up, under constant throttle. Noise goes away when I lift off the throttle. 2004 325ci, manual, 121000 miles. Anyone have an idea what is causing this? Thanks in advance!
Air filter box lid on properly?
Try adjusting the heater blower speed when it makes that noise. It might be something stuck in the vents that vibrates at an audible frequency
at that point. A dried leaf or something.
 

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Discussion Starter · #4 ·
Air filter box lid on properly?
Try adjusting the heater blower speed when it makes that noise. It might be something stuck in the vents that vibrates at an audible frequency
at that point. A dried leaf or something.
Thanks. Not related to HVAC blower speed.
 

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Discussion Starter · #8 ·
Drop your belts and spin your idler and tensioner pullies. Maybe they're on the way out or dry. If you hear any noise at all change them.
I think you're just going have to go through a process of elimination.
I did think of this, and appreciate your response. I changed the pullies and belt a few years ago. Hopefully they’re still OK. Maybe if it ever stops raining here in Pugetopolis I can pop the hood and check.
 

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Discussion Starter · #9 ·
Update: the sound only occurs around or below freezing. Another thing I noticed is that the SAP ran for a much shorter time than normal when it was below freezing. Could they be related? For reference, I’m in the suburbs East of Seattle where the winter temps are usually between 40 and 50 degrees. This sound (and the shorter SAP operation) occurred during a week where the temps ranges from 16 to 22 degrees Fahrenheit. Now we’re back to our 10th Pineapple Express with Atmospheric River of 50 degree rain and the car runs quiet. Also, there was never any performance change when it was making the noise. Engine ran strong throughout.
 

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Anti-Hack
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Still sounds like an air leak to me; that it occurs when cold is a snippet of supporting evidence: air gaps enlarge when cold, and gaskets become less pliable. Before picking up a wrench or buying a part, look at your fuel trims when cold; if LTFT varies inversely with engine speed, you likely have a vacuum leak. Above 10%+ can start whistling, but a CEL won't illuminate until 25%+. As a down and dirty test of your CCV (whose symptoms also exacerbate when cold), remove the oil fill cap with the engine running, in cold temps, preferably when whistling. The cap should be fairly easy to remove, with a little suction; if it freely pops off, or is difficult to remove, you have a CCV issue.
 

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RayMondo
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Update: the sound only occurs around or below freezing. Another thing I noticed is that the SAP ran for a much shorter time than normal when it was below freezing. Could they be related? For reference, I’m in the suburbs East of Seattle where the winter temps are usually between 40 and 50 degrees. This sound (and the shorter SAP operation) occurred during a week where the temps ranges from 16 to 22 degrees Fahrenheit. Now we’re back to our 10th Pineapple Express with Atmospheric River of 50 degree rain and the car runs quiet. Also, there was never any performance change when it was making the noise. Engine ran strong throughout.
The only thing I can think of that functions in response to intake temperature is the ICV.
Maybe there's a combination of factors like ICV position and intake flow rate.
A bit like blowing over the top of an open bottle. You only get a sound if you blow at a certain speed and a certain angle.
I just noticed in your video that the engine is till in the process of warming up and the ICV might be in play at that time.
Maybe it's not moving the way it should. A bit sluggish because it needs cleaning.
Bit of wild one I know. When was it last cleaned?
 

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Discussion Starter · #12 ·
Still sounds like an air leak to me; that it occurs when cold is a snippet of supporting evidence: air gaps enlarge when cold, and gaskets become less pliable. Before picking up a wrench or buying a part, look at your fuel trims when cold; if LTFT varies inversely with engine speed, you likely have a vacuum leak. Above 10%+ can start whistling, but a CEL won't illuminate until 25%+. As a down and dirty test of your CCV (whose symptoms also exacerbate when cold), remove the oil fill cap with the engine running, in cold temps, preferably when whistling. The cap should be fairly easy to remove, with a little suction; if it freely pops off, or is difficult to remove, you have a CCV issue.
CCV may be it. I’m seeing a little mayo under the oil cap, but just attributed it to my very short commute of less than 5 miles each way. I try to get it out on the freeway and get some hard WOT acceleration runs to a couple of times a week to help really warm things up. I’ll do the test you recommend. Thanks.
 

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Discussion Starter · #13 ·
The only thing I can think of that functions in response to intake temperature is the ICV.
Maybe there's a combination of factors like ICV position and intake flow rate.
A bit like blowing over the top of an open bottle. You only get a sound if you blow at a certain speed and a certain angle.
I just noticed in your video that the engine is till in the process of warming up and the ICV might be in play at that time.
Maybe it's not moving the way it should. A bit sluggish because it needs cleaning.
Bit of wild one I know. When was it last cleaned?
That makes sense. Yes, it occurs more when the engine is cold. In very cold temps (16 degrees Fahrenheit), it occurred even after running for 15 minutes. But does go away after longer drives which would obviously warm up the engine more thoroughly. Regarding the last time the ICV was cleaned, that would be…never. I’ll look at that this weekend if we get a break from the rain.
 

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RayMondo
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That makes sense. Yes, it occurs more when the engine is cold. In very cold temps (16 degrees Fahrenheit), it occurred even after running for 15 minutes. But does go away after longer drives which would obviously warm up the engine more thoroughly. Regarding the last time the ICV was cleaned, that would be…never. I’ll look at that this weekend if we get a break from the rain.
Rain sucks.
 

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I'm not sure, but intake leak, or something with belt wheels???
 

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Discussion Starter · #16 ·
Still sounds like an air leak to me; that it occurs when cold is a snippet of supporting evidence: air gaps enlarge when cold, and gaskets become less pliable. Before picking up a wrench or buying a part, look at your fuel trims when cold; if LTFT varies inversely with engine speed, you likely have a vacuum leak. Above 10%+ can start whistling, but a CEL won't illuminate until 25%+. As a down and dirty test of your CCV (whose symptoms also exacerbate when cold), remove the oil fill cap with the engine running, in cold temps, preferably when whistling. The cap should be fairly easy to remove, with a little suction; if it freely pops off, or is difficult
Still sounds like an air leak to me; that it occurs when cold is a snippet of supporting evidence: air gaps enlarge when cold, and gaskets become less pliable. Before picking up a wrench or buying a part, look at your fuel trims when cold; if LTFT varies inversely with engine speed, you likely have a vacuum leak. Above 10%+ can start whistling, but a CEL won't illuminate until 25%+. As a down and dirty test of your CCV (whose symptoms also exacerbate when cold), remove the oil fill cap with the engine running, in cold temps, preferably when whistling. The cap should be fairly easy to remove, with a little suction; if it freely pops off, or is difficult to remove, you have a CCV issue.
OK, it’s not cold today, mid-40s this morning. So not an ideal test. But I started the engine and as soon as the SAP had finished waking up the neighbors I removed the oil cap. There was no resistance at all. No suction or blow off. Is that normal?
 

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It's tough to qualitatively assess something over the internet, but there should be slight suction resisting oil cap removal.

Is your screech the SAP? It shouldn't be waking the neighbors.
 

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Discussion Starter · #18 ·
It's tough to qualitatively assess something over the internet, but there should be slight suction resisting oil cap removal.

Is your screech the SAP? It shouldn't be waking the neighbors.
There’s no suction at all.
SAP is super noisy but shuts off pretty quickly.
 

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There’s no suction at all.
SAP is super noisy but shuts off pretty quickly.
There should be ~10-12 mmHg vacuum at the oil cap, a little less than normal engine vacuum. So if you're seeing no qualitative vacuum, explore a CCV failure.
 

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Discussion Starter · #20 ·
There’s no suction at all.
SAP is super noisy but shuts off pretty quickly.
There should be ~10-12 mmHg vacuum at the oil cap, a little less than normal engine vacuum. So if you're seeing no qualitative vacuum, explore a CCV failure.
Ok, checked again and there is suction. Sorry that was misleading. I guess I’ll just have to wait until the next cold snap and see what happens. Car runs great for now.
 
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