I think I can here ya KNOCKING!

OK, a few questions: original trans? IF so, look at your flex plate. I bet its cracked if its the original trans and no 1/8 thick bushing was used on snout. Mine broke 3 ears and kept working until I threw a piece out on the freeway, bounced up and hit the floor with a loud clack and bounced down the road behind me. Remove 1 convertor bolt at a time and see if any ears fall out. Running headers? Check for heat pulses around exhaust flange while running. 3rd, just drop the pan and start jiggling rod caps. Itll be quite obvious if there is a bad bearing.