[big gear head]

Most of the time this type of problem is due to old oil. The clutches in the differential are not slipping smoothly and causing the noise that you are hearing. Many times simply changing the oil and using the correct GM limited slip oil additive will cure the problem. It may take about a week for the new oil to completely fix the problem, so give it little time.

While you have the brakes off you can do a simple check to see how much the clutches are worn in the differential. Pull and push on the axles and see how much they move in and out. If they move more than 1/16 inch then they need to be shimmed or replaced. If this has the Eaton Posi in it then most of the time shimming the clutches is all that is needed. If it has an Auburn then replacing the differential is the only way to fix it. Axle end play is important when using disc brakes. When the axles move in and out it pushes the caliper pistons in and can cause problems braking.