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Discussion Starter · #1 · (Edited)
When my car is started cold, it makes a weird high pitched noise - I can't decide if it's a whistle or a mechanical squeal. I read lots of threads describing similar issues and it seems most are either caused by pulley bearings or vacuum leaks. Armed with that knowledge I had another look and recorded a few video clips. I noticed that the noise gets louder as I crack the throttle a little, but disappears as I accelerate. Then it comes back when I close the throttle. But, the pitch doesn't go up with engine speed as you might expect it to if it was a pulley related noise. All of that makes it seem to correspond with vacuum.

Still, sometimes it does sound more like a squeal than a whistling noise. In any case it disappears completely once the engine warms up.

What do you guys think?

A clip taken from the engine bay:
https://www.youtube.com/watch?v=DsXk1hhXsEg&feature=youtu.be

From inside while driving in 1st gear:
https://www.youtube.com/watch?v=Yk5Uch51f_U
 

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You have a bearing on the serpentine belt that is about to fail. Take the belt off and start the car. If the noise is gone then I am right. The belt has an idler and a tension pulley that both can be the source of the noise you have. You could also have trouble brewing in the alternator, but my money is on the idler/tension pulleys.

You have to remove the belt to the AC, then remove the main belt. This will put you in a position where you can start the engine and listen for the noise to be there or not be there. You will not have a cooling system while the belts are removed, but you get a few minutes of run-time before the lack of a cooling system comes into play.
 

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Discussion Starter · #3 ·
You have a bearing on the serpentine belt that is about to fail. Take the belt off and start the car. If the noise is gone then I am right. The belt has an idler and a tension pulley that both can be the source of the noise you have. You could also have trouble brewing in the alternator, but my money is on the idler/tension pulleys.

You have to remove the belt to the AC, then remove the main belt. This will put you in a position where you can start the engine and listen for the noise to be there or not be there. You will not have a cooling system while the belts are removed, but you get a few minutes of run-time before the lack of a cooling system comes into play.
I don't have the tool to remove the fan right now, but I reached in and checked the highest idler pulley - the one mounted just above the alternator. Even without removing the belt I can feel a little play in it. So maybe that's it.
 

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2003 M3 6MT Slicktop
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can't open your vid at the moment, but if it's a whistle only when cold it could be the secondary air pump
 

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Discussion Starter · #6 ·
You have a bearing on the serpentine belt that is about to fail. Take the belt off and start the car. If the noise is gone then I am right. The belt has an idler and a tension pulley that both can be the source of the noise you have. You could also have trouble brewing in the alternator, but my money is on the idler/tension pulleys.

You have to remove the belt to the AC, then remove the main belt. This will put you in a position where you can start the engine and listen for the noise to be there or not be there. You will not have a cooling system while the belts are removed, but you get a few minutes of run-time before the lack of a cooling system comes into play.
Well it looks like you were right :) I just replaced the 2 pulleys on the main belt and the noise is mostly gone. While I was doing it I noticed that the AC pulley is shot too but I don't have a new one yet. There's still a faint whirring noise which I presume is the AC pulley but it's a big improvement. The 2 I removed were definitely past it.

can't open your vid at the moment, but if it's a whistle only when cold it could be the secondary air pump
Good point. Now that most of the noise is gone I was able to discern the SAP noise and it is kind of similar. I could hear it shutting down after around 30 seconds or so. But there was still some noise so
 

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if its making noise doesn't mean the bearing is going to fail, thats like saying the sun is going to supernova. The bearing is just dry and will have accelerated wear, if not taken care of in a timely mannor. Soon as mine started making noise I took it out and gave it a nice cleaning of any leftover grease, inspect the bearing for damage and repack it with good quality grease. Mines been going strong for 4 years since I did that.
 
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