truck pops out of reverse when gas is applied and make a horrid grinding noise on 1996 Chevrolet Suburban 1500

truck pops out of gear and makes a horrid grinding noise if gas is applied when in reverse. Does not do this in forward gears at all. It will idle backwards. This is an automatic trannie.

Sounds like fan hitting shroud from a bad motor mount allowing the engine to torque and lift when accel in reverse. Check that out asap.
1 more answer , 1 more comment
motor mounts ok?
motor mounts will not make it pop out of gear.I have the same problem and its my rear end.