Originally Posted by Stevo86
Tremec makes the TR-3650.
That kind of thing is gonna be real tough to diagnose on the internet but my guesses are driveshaft out of balance or something in the rear end. Maybe an output shaft bearing.
Take note of whether it is accompanied by a vibration, if the frequency of the sound changes with vehicle or engine speed. Or if it changes with gear shifting. If you really listen to the sound and think about how everything works together you can usually narrow it down. Good luck
He doesn't have a 3650 he said he has an automatic