LittleBeast - Are you talking about the automatic tensioner pulley? (Ider arm?) Or a stationary routing pulley? Also, sometimes you can track down a bearing or belt that's making noise by shooting either a little water, or belt dressing on the suspeted areas until the sound goes away or changes...

My a/c compressor pully (I suspect) just started making noise yesterday as well... After I got it wet during the water manifold gasket change. The noise comes & goes, but it sounds like the magnetic clutch for the a/c is dragging. It'll go away immediately when I turn the a/c on, but it still tends to come & go after that.