Odd squeal coming from front, increases with acceleration

98 540iA has some odd squealing sound coming from what I believe to be the front under the hood, and I'm just not sure what the heck it is at this point. I've done a bit of searching on the forum, but nothing looks to be ringing a bell or matching the symptom.

Seems to be aggravated by the cold, not as likely to happen when warm out... Definitely not the brakes, much higher pitch than that (and I checked the pads as well as their backs to be sure this wasn't the culprit.

Once the car is fully warmed up, everything seems to be fine (not just engine temp, as it takes 5-10 miles or so after temp needle reaches 12 O'Clock). Only thing I can think of at this point is either something related to the drive shaft (?) or perhaps a wheel baring (though I don't know what that would sound like).

Is there anything common that I might have missed or any possible suggestions anyone might have? Difficult to narrow the dang thing down as I have to be moving to hear it and only REALLY hear it after 15-20mph and up :-(

Hope everyone had a decent weekend!

Something I just realized I forgot to mention: while I thought it was likely unrelated, I turned the fan up a few notches, then all the way off - no noticeable change in squealing

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Still trying to narrow this down... It's weird that it only happens in the cold. I'm getting to the point where I'm about to just replace the front brake pads anyway on the off chance this is what's doing it.

So far I only know it has to do with SOMETHING rotating as it only happens after getting under way lol

Could it be your serpentine or A/C belt? Perhaps one of the tensioners has worn out.

+1 on the belts and/or tensioners as the most common cause of squealing.

Is the noise engine speed or road speed related?

It may sound weird but try melting some wax onto the Serpentine Belt, or spraying some WD-40 and see if the sound goes away. if it does then it's probably your belt tensioner.

I'll give that a shot next time I drive it. Might be the weekend as im still milking two wheels as much as I can :-D.

It appears to be relates to road speed though, not engine speed, which led me to something wheel or drive shaft.

I'll update once I have anything of note.

Thank you all for the input!

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Well, I pulled off each wheel and did a ton of lubricating on anything that looked like it needed it. Pic attached of mid-process :-)

No dice. One thing that did come to mind - I replaced the later OEM Textar pads with Jurid pads in the rear and these cover a larger part of the rotor than the Textars did. I thought perhaps the squeak was related to the wearing of the rust ring around the rotor by the new pads, but this has since worn down and the squeak persists.

Now I'm wondering if having the Textars still up front and the difference in grip is what's screwing with me. I check for free rotation up front and it seems fine. There's some tension in the rear in neutral, but this is expected. Still nothing catching that I've found.

I'm going to continue to tinker and plug away. Maybe I'll start going through the process of upgrading the braking components while I'm at it :-)

Check for hitchhikers.

Is the sequel related to road speed, engine speed (revs) or acceleration/throttle position?

If it revs need to look at belts, pulleys etc. Acceleration I be looking a vacuum leak on the engine. Road speed i be looking at brakes and suspension, running gear etc.

I mentioned it earlier, but it is a ways up in the thread. It seems to be road speed related only. It also goes away after 10 minutes or so of driving which I thought was weird, probably related to moving parts warming up...

Secondary Air Pump?

As it seems to be directly related to road speed, I'm not sure how it could be the secondary air pump... Though I could easily be missing something. Could you clarify?

I'm just spitballin'

Mine gives a quick squeal in cold weather only but I have heard others say that theirs has acted similar to what you've described. I also had a wicked bad tear in my intake boots that caused a nice falsetto on acceleration. but happened all the time and was temperature independent.

How are your forward inner fender liners? If they are damaged or missing? Your pump could get gunk on it and cause it to act weird or straight up fail. When I bought my car, they were both missing and I never drove it in wet or snowy conditions until I replaced them.

Fender liners are all in place and in good shape :-)

A good deal of the fun for this car (at least for me) is working on it. I refuse to give up till I find the problem lol

I'm actually wondering if a wheel baring could cause something like this squeak at this point... Though in my experience if a baring starts going, it's a grind and not a squeak.

Can you take video of sound?