Is there some sort of problem with the rear axle bearings and/or the differential cover gasket?
If you look at the rear differential cover, you will notice two small indentations on either side directly in line with the axle tubes. These indentations are to direct the flow of oil through two holes in the differential case which then flows down the axle tubes to lubricate the axles and the outer axle bearings. The differential cover gasket is also supposed to have two holes in it, which line up with the holes in the case as well as the indentations to allow oil to flow down the axle tubes. Starting in the 1990 model year, GM has been improperly installing differential cover gaskets THAT DO NOT HAVE THE LUBRICATING HOLES!!! If you do not change this gasket to one that has the proper holes, your outer axle bearings, as well as the axles themselves, will be destroyed by around 70K miles. The damaged (under lubricated) bearings will wear grooves in the axle shafts, requiring that they also be replaced. If this is left unchecked, the metal bits from the damaged outer bearings and axles
