Grinding when off the throttle

[Swamp82]

ok so got the truck running good enough to take it for a drive today and and when i let off the gas there is a nasty grinding noise (sounds like gears grinding) i get back on the gas it stops, also when i let off and it starts grinding if i manually downshift while its grinding it stops making the noise ..so i went home and removed the front drive shaft just to see if there was any change..and nope no change. good i cant hear for sure where its coming from but the fact that it stops when i downshift leads me to think a transmission problem? its a 700r4... any help would be greatly appreciated.

[Engineer]

I am afraid you are correct- tranny problem.

If it were the coast side of the rear axle ring+pinion it would do it in all gears.

[Swamp82]

yeah it seems to be just in overdrive and drive at about 30 mph and up..

  thanks