I'm on Challenger No 5, and all of mine has been rattlling, convertibles (I had 3) rattles more. I put subframe connectors in the convertible I have now, and that took care of a lot of it. Still clunky in doors, trunk etc, and I never rebuild the suspension on one until now, so I'm excited to see how it drives next summer. Later on I will try to get the doors tight, take apart and fix, its not exactly a Mercedes click when I close my door now... The e-bodies rattles way more than Mustangs for example (I had 4 Mustangs also).
Btw, I also think the way the interior is made, big plastic covers over steel construction, is actually acousticly amplifying sound rather than damping it, so a good sound deadener, Dynamat or something, is on my list also.