If the noise appeared the same time as the repair, there's a very good chance that it's related. Check the sheet metal inspection cover on the transmission to make sure it isn't contacting the flexplate bolts or something. The torque converter balloons slightly as power is put through it, and it may be enough to contact the cover under load. Another thing to check is that the engine and trans are in the same position as before the work. If things shifted slightly during the installation, you may be getting interference with other components. May have even damaged an engine mount, that sort of thing. See if you can duplicate the noise with the trans in gear, foot on the brake and a bit of load on the engine. Careful!
