Check the belt tensioner pulley for wobble or any indication that the bearings are about to fail.
With the belt off you can check each pulley for noise when you spin them by hand (this should help you locate the problem).
By the way, Is the a/c on when you hear this noise? If so, try it with the a/c off to see if it goes away.
Tuesday, August 5th, 2014 AT 6:25 PM