Symptoms:

I got new tires put on. While driving from the tire store, I went over a bump. Associated with the bump (railroad track) I heard and felt a loud “smack” sound. I thought it was a tire weight. While driving to the tire store, a severe, intermittent, vibration came from the transmission area. So I went and had the tires re-balance. While driving on the freeway, I heard and felt a banging sound when the car de-accelerated. Also, while stationary, there was a vibration/grinding noise in reverse. I check the fluid and it was about ¾ quart low on a up hill slope. I logged onto this board and listed these symptoms. It was recommended that I:
1) Check the transmission mount
- It was broken, I replaced it, but symptoms remained
2) Check the driveshaft, center bearing and U-joints
Upon checking, everything looked good. But I replace the bearing, rubber mount and spring, and all three U-joint. The symptoms still remained.

Following this I replace the motor mounts (one broken). However, the symptoms remain.
Next the transmission pan was removed. The fluid looked ok, no metal


In the mornings, when the car is cool, the transmission sound normal. After about 5 minutes of driving, and associated with going over a several bumps, the grinding vibration starts and then increases in severity. The pan was pulled off and the transmission was clear of metal and pad material. There was a slight burnt smell

Any ideas on what this might be? Flex plate? Torque Converter?