Rear End noise getting louder

I wanted to run this by the experts on this forum. I have a 2008 TRD DC Auto. I am noticing when driving on the highway and I let off the gas there is a whining noise from the back of the truck. As soon as I even touch the gas peddle the noise goes away.In my experience this has been the differential. Any way I can test or verify? When I make sharp left turns I also hear a grinding noise. Dealer is no help since every thing to them is normal.

 

Sounds like inadequate gear lubrication or improper backlash. Drive your truck for 15-20 min, then feel the diff. If it's too hot to hold your hand on there then the gears most likely need replacing ESP if you're hearing grinding. If it feels warm but not hot, maybe drain the diff lube through a collander and look for debris- also a sign the gears or bearings are in trouble. The longer you go without correcting this the worse it will get.

 

Also if you're losing diff oil it can only escape through the diff cover flange or through the axle tube seals. Do you have an oil spot under your diff? If so it's the cover flange. If not check the left and right side ends of the axle tubes for leakage.