There are ways to diagnose the differential just by the noises it makes. I replaced mine @43,000 because it had a light throttle whine above 65mph. I haven't opened up the old diff but am sure it's the pinion bearing. Dependant on ring/pinion wear it is rebuildable with a new bearing and some good knowledge in setting up backlash. Hopefully yours is an easy fix. The differentials are easy to drop out and replace. Don't let the shop dismantle the rear suspension to do it, adds time, requires an alignment and is un-necessary.