[Hocrest]

The flexplate bolts to the back of the crankshaft on the engine, the torque converter in the transmission bolts to the flexplate. They can sound like that, and since it attached to the crankshaft, it is always spinning independant of what gear you're in.

Since you are getting the trans out anyway, it makes that an easy thing to check. They are the same flexplate used in some newer soobs, so many dealers have them in stock.