Rear End Noise 2002 Isuzu Trooper

Question

I have a 2002 Isuzu trooper ltd - rear end roar and noise at speeds around 65 mph usually and it was very cold a few weeks ago and at around 40 the roaring noise was very loud.  During the summer I have noticed that when I go through the cars wash it is very quite for a bit then same deal.   

Have heard that it could be bearings in the rear or pinion bearings or universal joints…  A shop replaced the U-joints last week and that caused a new issue…

it now has a vibration at 55 plus and still makes the noise.  

The vibration has a low rumble as well and you can feel it in your bones.  Shop put it on a lift and we went under it while guy ran it up to speeds of 55 plus.  No roaring noise (no load on the wheels either) but the transfer case sounded like it had rocks in it.  Not real bad but it did not sound good.  

The shop checked all the fluids and levels.  All levels were great and fluid was very clean.  I knew this because I keep it in top shape. Thank God!

Has 75k miles on it and about 4 months of extended warranty left.  I bought it used from a Ford dealer and bought one of the better extended warranties.  The warranty company is very good and they will fix it if we can find the problem.  I’m taking it to a specialty shop this coming week for them to check out.  

Does anyone have some info which would help solve this puzzle?  Much appreciated
Thank you - Shawn