Hm... it looks a bit dirty. $50 for one ain't bad. So, I'm going to be replacing the idler pulley, serpentine belt (some weather checking on it), IAC valve, and will be taking it to the mechanic that did the bearings (he claims that he replaced inners and outers and warranties his work, so I'm going to bring it up to him tomorrow to have him take a look). Hopefully one of these things fixes it! I also read about pinion bearings causing this, but don't have much experience with differentials, any chance it could be bearings or seal?