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Old 05-20-2010, 01:58 PM
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bluebee bluebee is offline
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Location: San Jose, California
Join Date: Mar 2008
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Mein Auto: 02 BMW 525i M54 auto 130K
Originally Posted by Fast Bob View Post
Take a spray bottle with water in it....spray a little on the idler pulley....if the noise goes away, the pulley is bad
I soaked the idler pulley and then the 6-hills-5-valleys serpentine belt with Wisk. The noise abated but only slightly, and since it's intermittently loud and silent, I couldn't tell a thing from that test.

I can't imagine a stethoscope working safely because of the moving parts (I mean, you can't just put it on a pulley, can you?) But I'm looking online in AutoHauz for the stethoscope as I'm getting the cabin air filters anyway).

Luckily, I need to replace the serpentine belt (it has cracks); but while I'm at it, I'd rather not take it apart twice so may I ask what is the total list of possible components that could cause the intermittent squeal?

- idler pulley bearings (can be repacked with grease, right?)
- alternator bearings
- water pump bearings
- power steering pump bearings
- the 5-ribbed (6 valleys) serpentine belt

In cn90's diagram, I see a few more parts (do you think they have bearings that could cause that noise)?
- idler roller
- two other rollers
- hydraulic tensioner
- ???

I hate to take it apart twice just so it would be good to diagnose before getting all the parts. I will try the suggested 2500 rpm test if I can get a helper so that I can videotape the noise.

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