I have searched based on my problem and think this might be the carrier bearing in the driveshaft.

A few weeks back while driving the car ~50mph I heard a hard clunking sound that appeared to originate from the rear passenger wheel area. I immediately slowed down to a full stop and it sounded to be based on some type of rotation speed. As I slowed the sound subsided.

After coming to a full stop the sound was gone and when I continued to drive again the sound had disappeared. I thought that perhaps I picked up something on the wheel and it came free after stopping.

Fast forward to last night. While driving on the highway ~70mph the vibrational sound came back, but appeared to originate from the tunnel between the front seats. It sounded violent so I immediately slowed. As I slowed the sound lessened until I came to a complete stop. Started again and the sound was gone until I reached ~60mph and the sound returned as if something was banding around in the driveshaft tunnel.

This is a violent sound that resets itself once I come to a complete stop. After 3-4 times of this happening I was able to limp home at ~45mph without it repeating. I am heading out of town for a few days and will check driveshaft and rear CV axles when I return, but if someone thinks they know that would be great.