IMO...
Try going down a long gradient, say on an Interstate road at speed, shift into neutral and coast for approx 1/8 mile or so. Check for noise. While coasting down, and traffic permits, try some gradual left/right steering input, say like you're changing lanes. Listen for noise....if noise occurs, when inputting a left turn, it is likely that the RIGHT side rear axle bearing is failing. If the noise occurs when turning right, the left rear axle bearing is the noise source. These maneuvers loads the rear axle bearings while they are rotating at speed.
Yes, it is possible that one of the differential carrier bearings are going bad, but is more probable. The differential pinion bearings are just rotating and should be quiet under these conditions without any or nomimal thrust load. The choice of rear axle bearings not withstanding, a failing ball bearing assembly will present this way when subjected to rotary and AXIAL loads. The FSM procedures should be followed to make the final determination. Just my opinion of course.
BOB RENTON
