Had a whining noise coming from the belt area on my 2003 n/a Bonnie and from this forum sounded like I should change the tensioner pully. Bought one from the auto parts store and when I put it on it did not work. Looked very close but the contour of the bolt side of the pully was slightly different causing it to bind when I tightened the bolt. Took it back and then went and got an AC delco one. Same problem. I ended up pressing out the bearing on the new one and pressing it into the old pulley. This turned out fine but the bugger is that I still have the whine. After listening closer it sure sounds like the alternator.
I just installed an idler pulley for the */C. It the one with the ribbed for the inside of the belt. Anyway, I had kinda the same issue. The large washer that covers the pulley would not let the pulley spin. So i omitted the washer. The bolt head was big enough to cover the bear. We will see what happens. There wasn't enough left of the old pulley to press the new bear in and out. Thats a good idea though.
Take a LONG screw driver and put the end of it on each belt driven comp. Make sure its long enough so you are not close to the runnning engine. Listen for a difference in nosie on each, Then take off the belt and spin each pulley by hand. you should be able to verify where your noise is.