I would first recommend to drain and fill the rear differential fluid. Believe it or not, the fluid will break down and not lubricate the gear assembly properly in the rear differential. When that is the issue the noise usually showes up when doing u-turns or sharp turns.
A+ Japanese Auto Repair, San Carlos Ca 94070
I had the same problem right after service from one Dealer. I brought to another and had them inspect, the technician drained the fluid, drove the truck in a figure 8 pattern outside for about 5 minutes, then changed the fluid again.