Hard throttle transitions, bearing noise...ideas?

[jaybreitz]

Hey guys, wondering if anyone has experience with this. I tried searching, but nothing really matched my issue entirely.

Heres my problem: '90 NA, MT. started developing hard thottle transitions, like theres alot of slack in the drivetrain. First thought was motor mount, second was differential bushings. It feels like either of those, but they seem to be in good condition. Around the same time, it started to sound like a bearing was letting go...high frequency grinding, most noticable under hard acceleration but always present. The noise stops entirely with the clutch pedal depressed at idle.
I also noticed when the car is moving in first gear around idle, when the entire driveline is moving at roughly the same speed not under any acceleration or deceleration, theres the sound of gears mashing together. Its definitely not a good noise, but the whole situation is kind of hard to explain.
Has anybody had any experience with this? Im sure someone has to, because ive had the SAME EXACT problem in the turbo Z i just sold. I sold it as is, i never figured it out.
-A mechanic friend suggested the clutch disks in the differential, but that doesnt explain the bad bearing noise stopping with the clutch pressed.
-I believe it could be the countershaft bearings, but the PO says it has a brand new trans.

Im stumped. Any thoughts would be greatly appreciated!

[J30tChumpCar]

Sorry there are no clutch disks in the differential, a guess from your description, the transmission is on its last leg, most likely the input bearing, inspect fluid for metal, if you want to fix it stop driving and pull the trans for proper inspection before trashing it any worse.

[t.mcginley.jr]

Definitely sounds like a trans problem. Good used manual transmissions are pretty cheap, usually $200-400 MAX