One potential suspect is one of the flex plate-to-torque converter bolts is hitting the webbing on the back of the engine block, or the inspection cover is bent or not positioned properly. A clue is the noise will get worse under relatively hard acceleration or load because higher line pressure can make the torque converter balloon up, or expand slightly.
The flex plate can get bent too if the torque converter slipped off the input shaft, then got forced back in when the bell housing bolts pulled the transmission up to the engine block.
You might be able to locate the source of the noise with a stethoscope, but if it only occurs when you're driving, there's tool called the "Chassis Ear" that will help. That's a set of six microphones, a switch box, and headphones. You place the microphones near suspect points, then switch between them while driving. Be aware that many mechanics have never seen or even heard of this tool. Suspension and alignment specialists use it to find squeaks and rattles. You may find this tool at auto parts stores that rent or borrow tools. I've seen them on Amazon too. The newer model uses four wireless microphones and two of the standard wired microphones.
Saturday, January 24th, 2015 AT 4:55 PM