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Re: unidentified noise in 90

> Lately, I have noticed a strange grating noise at certain RPM in 88 90
> (80,000 miles).  It occurs only at 2000 and 2700 rpm.  It seems to be
> coming from the area of the alternator, but I am not sure.  My mechanic
> seems to feel there is no serious problem, but I hate any untoward noise
> coming from my car.
> Any ideas?

Grating noises shouldn't be ignored - they may spell trouble. Most likely,
the bearings in your alternator or any one of the belt driven accessories
(hydraulic pump, etc) may be going bad and may disintegrate. Try to isolate
the noise and find the culprit. With a grating noise, you may be able to
feel vibrations on the body of the alternator (or pump) with the engine
running. Be extremely careful while doing this - keep fingers away from
the moving parts. Another test you can do is to grip the alternator pulley
(engine not running of course) and see if there is any lateral play. If the
pulley moves laterally, then the bearings are shot. The belt may have to be
loosened to get best results. Generally, bad alternator bearings first
start off by making a high pitched whistling noise that varies with engine
RPM. Then it worsens to grating noises as the bearings wear down.
If it is the alternator, the best bet is to replace with a Bosch remanufactured


Zafer Mehmood				   AT&T Bell Laboratories
zm@mhcnet.att.com			   Murray Hill, NJ