I have a grind that I think is coming from the rear axle but it is hard to tell for sure. It is most noticeable when I am turning uphill, like when pulling out of a parking lot onto a road that is higher. At first I thought it was the lack of friction modifier in the rear axle (Royal Purple fluid) so I added some but it did not help. What else could it be? Clutch packs?

It also happens when turning on flat ground when I first start up the truck.