Have a thumping sounds that I believe is coming from the rear differential. Took to the Dealer who after advising to replacing the front and rear u-joint (which I did and didn't take care of the nois. They now recommend that I replace the differential. Dealer changed the fluid to "diagnose' the noise and discovered alot of metal and said the spider gear was loose (by visual inspection and moving with a screwdriver). I don't have a high level of confidence in the dealer diagnosis. I have had the truck for over 2 years and it has always made this noise never getting any worst. It sounds like a low thumping bad bearing. It's intermittent and happens at random times (under throttle, no throttle, low/mudium speed). Just drove a 2K mile trip with no issues. Super low miles on truck and rear end 68K. Truck has not been used to tow or carry any significant weight as far as I can tell. Would running heavier gear oil help? Looking for any suggestions . Cheapest I have found an OEM new rear end is around $1K. Would hate to go that route.