Pull the rear inspection cover off the rearend. crack it open and let the lube drain. On my diff the small spider gears in the center were scared pretty good. The ring and pinion had small scratches in wear surface. 99% sure that is the cause of my noise. Ring and pinon not messed right. Had an offer for a free rear diff that only has 50,000 miles but it has 4:10 gears which I don't need. Iwould love to have a 3:55 but I think they only come in the 10.25 rearends.