Dribble a little water on the smooth back side of the belt while the noise is occurring. If the noise changes, check the spring-loaded tensioner to see if it is sticking and not putting enough tension on the belt, and check for pulley misalignment. Typically that will also be caused by a worn pivot for the tensioner pulley. If the belt is off-center by as little as 1/8" on any pulley, that will cause it to slide sideways across it as it goes around it.
Based on your observation that the noise stops in short order, it's more likely to be a tension-related problem. Some engines use a separate belt for the AC compressor. Be sure to check that one for proper tension too.
Monday, June 20th, 2011 AT 9:10 PM