manual transmission replacement ????

Just installed a used 5spd transmission in my 96 civic, if i accelerate then release the gas I get a very loud humming sound. It happens in every gear when there is a load on the transmission and the gas pedal is released. If I continue to accelerate I don't hear it. Is this tranny shot??? did not have this problem with the old tranny. the old one ran with no oil and started to grind so I put in a used one. any help???

check your fluid level.

Sounds like a bad bearing in the transmission.
But it could also be a CV joint so I'd check that out first.:smokin:

you say you have it in gear and pushing clutch? maybe throw out bearing? usually cv joints make sounds like that when you turn if they going bad.