When I'm going around 70-80 on the highway, my car vibrates constantly whether I push the accel or not.
Might this be something related to the exhast? 'Cause one of my mufflers has been damaged slightly...after I got into an accident few months ago...
Any suggestions?

 

Your wheel balance is off....maybe a bent rim. Go have those ADR's re-balanced. If that isn't it then maybe your alignment.

MW

 

a search would find this