Please help with noise diagnosis....

[75Chevy90Kawi]

i asked this in the engine/drivetrain forum, but in 3-4 weeks i got zero replies. and you guys have helped me before

first off, it's got the original th350 in the truck, but it was rebuilt when the crate motor was dropped in by the previous owner, which was about 8k (i think...) miles ago.

in january i dropped the tranny and replaced the torque converter after the bolt holes stripped. before they stripped, when i shut it off, about 3/4 of the time it would make a sort of clanging noise a few times when i shut it off.

a few weeks ago my truck started making a bad rattling/buzzing noise at about 1300 and 2300 rpm, (and a little bit every once in a while at 700) and two or three times has made the clanging noise like it did before, although not as bad (dont think it's a high idle either, but i do need to adjust the timing a bit, i just dont have a timing light). as far as i can tell all 3 bolts are in the TC good and tight, and although i havnt looked very closely, i cant see any cracks in the flexplate.

i havnt really driven the truck in a few weeks because i want to find out what's wrong before i REALLY break something. i THINK it only does this in gear, but since i havnt driven it in so long it may be that it does it in neutral and park as well (but i'm pretty sure it doesnt, i'll check tomorrow).

i have yet to go through and check the drive train all the way from crank to rear end, (also something i need to do tomorrow) but was wondering if anyone can offer any insight into what this could be.

you guys have been big help before. one more time perhaps?

thanks
mitch