Dribble a little water on the smooth back side of the serpentine belt while the engine is running and it's making the noise. If the sound changes, it's the belt. First look for any pulley that is tipped and making the belt out-of-alignment. You look for that by looking for anyplace the belt is peeking out to the side when you sight along all of the pulleys. A tipped pulley can be caused by a mispositioned component but more commonly it's due to a worn bearing in an idler pulley. The bearings can make a chirping sound too. The tipped pulley causes the belt to slide sideways across it as it goes around it. Don't use any type of belt dressing on serpentine belts. That will make dirt stick to it and the noise will get much worse.
Also check that the belt is tight. You should probably do that with the engine not running! Tug on it and watch the spring-loaded tensioner pulley move. It should move back smoothly when you release the belt.
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Saturday, April 7th, 2012 AT 4:22 AM