You know we can't diagnose that over a computer without a lot more details or observations, but the common causes are worn bearings in an idler or tensioner pulley for the serpentine belt. Alternator bearings will do that too but they're a lot less common. Remove the belt from the crankshaft pulley, then run the engine long enough to verify the noise is gone. If it is, you know it's related to something driven by that belt. Usually you can pinpoint the source with a stethoscope. If you don't have one already, any auto parts store will have them for about ten bucks.
Tuesday, April 24th, 2012 AT 10:42 PM