I guess I'd suspect a noisy pinion bearing in the differential first. A tool that might help is called the "Chassis Ear". That is a set of six microphones, a switch box, and head phones. You switch between the microphones and listen while you drive to hear which one is closest to the source of the noise. You might be able to borrow this tool from an auto parts store that rents or borrows tools. Be aware that many mechanics have never seen or even heard of it, but most new car dealers have them.
Put one microphone on the differential, one on the tail housing of the transmission, and if you have a two-piece drive shaft, put one on the center bearing too.
Wednesday, July 13th, 2011 AT 8:23 PM