Grinding noise in reverse.

I recently did a trip on the Trans America Trail from Georgia to the Mississippi River in my 2017 Tacoma SR5 < 60,000 miles. While on the trip I m noticed a grinding noise when I put the truck in reverse (not moving and backing up) and a vibration in the excelerator around 2000 RPM going foward. The noise and vibration seems to subside after the truck has been driven for awhile but returns when the engine/transmission is cold. Took it to the dealership but they said they could not duplicate the noise or vibration. I have been told it is possibly the U joint. Anybody else had a similar experience

 

Were there any water crossings on that trip?
If so, how deep?

 

You can always physically inspect a U-joint for looseness and usually a loose U-joint will not cause a grinding noise. Any mechanic worth his salt can tell immediately if a U-joint goes bad.

 

Yes 2 knee deep one, water was up to the rock sliders

 

Did you do the diff breather relocate on the rear axle? If not, I would change the rear diff fluid asap.

 

I thought I heard a grinding noise. turns out it was my neck when looking backwards