How about posting a few pictures of the exhaust
including a good shot of the exhaust hangers? Maybe the pictures will be worth a thousand words for a possible cure. A few things to think about regarding e-body applications. There is not enough room for the proper size mufflers under the rear seat where the original short resonators were installed. Short 14" case mufflers are not going to abate interior resonation. There was a reason why the Chrysler engineers placed the large round mufflers in the rear next to the fuel tank and the resonators under the rear seat.
Engine and transmission mounts not made of the proper insulating rubber can also add to the existing resonation problem as well. Just a few thoughts.
