[SeaSlugs]

Yea you need to do some diagnosing. First steps pull floor and inspection cover on bellhousing.
Next start engine with clutch depressed in gear.
Listen for any noises
Then shift to neutral and slowly let the clutch out
Listen for any noises
If everything still sounds OK carefully go for a short drive around the block/your yard and listen for any noises.

report back what you hear when you hear it and note clutch position, gear your in, and speed.

Could be anything from piolt bearing, throwout bearing, trans bearing, spedometer gear/cable, starter bendix, belt squealing in front of the engine, water pump bushing/bearing, generator bushing/bearing. All those can make noise and sound can travel to far away places so it may have sounded like it came from the trans but in reality somewhere else hence remove floorboards and inspection cover to help pinpoint it.