FYI, something you might check. I have had on both Challenger's I've owned, a deep rattling when driving on a rough dirt road. I was snooping around and when I had the tail lights out, I reached down into the inside of the bumper cover and discovered that the hard plastic energy absorber that runs the length of the cover has some play to it and does rattle a bit. Just a thought.
MSgt, USAF, Ret. 1977-2001
Crew Chief A7D, A37A, A10A
2010 Hemi Orange RT 6 spd - gone
2012 Header Orange RT-C 6 spd - gone
2013 Jazz Blue RT auto - gone
2014 Header Orange R/T Plus 6-spd - here