Sr20det transmission issue vibrations/resonating 5th gear...

[Vr6WantSr20det]

Initially with my first motor/transmission put into my 90hatch, was a blacktop s13 with 5sp transmission. Since day one the transmission made a sound in nuetral as if the mainshaft bearings were going. Also when reving too high or putting good amount of load while engaging the clutch it would grind, as if you miss-shifted but it's already in gear. When i would press the clutch the sound would go away.

-Well i had the transmission replaced 3 weeks ago, and once in a while it would make the same noise as if the mainshaft bearings were going. It shifts smoothe and doesn't grind. When the sound does come back, i would need to press/depress the clutch and it would go away. TOB/PP/Flywheel??

-Starting about 2-3 days ago as i'm on the highway in 5th gear, I noticed vibration/resonation in the engine transmission. I'm used the 4th gear decelerating sound from 3k-2.5krpm. due to the act 6-puck un-sprung clutch and HD PP. So in 5th gear on the highway while it's making the vibration/resonating sound i will press the clutch in, and depress it and the sound/vibration will go away. I just need to know if this is most likely a transmission issue, as it's about 3 weeks old and i can get a refund/replacement. Or is it somehow a throw-out bearing going bad(clutch/pp/tob 1yr old.). Someone also suggested loose flywheel bolts but i would assume that would be vibration/resonance in ALL gears, and not just 5th. Thanks for any help/info.