somewhere down that long thread it got hijacked. There is some talk about the engine smacking the firewall on hard takeoff (drag racing). I am accelerating quite slowly. I would only expect noise if one of the mounts had torn badly. It looks like you need to get the car up on a lift and remove the skid plate to inspect that portion of the car. I only have a driveway/garage to work in. It's snowing right now so I'm not going to climb under today.
Does anyone have any other ideas what it might be?