I did the same exaust mod on my R/T automatic with the Flowmaster super 44's. However, I had an x pipe installed. All for a little over 500 bucks. The sound is awesome! I'll post video soon. Great sound on your Challenger. Also, this mod unrestricts your exaust, so expect some HP gains. Congrats! Interior noise is not too bad, some drone in the lower RPM, but just a sweet, low rumble at highway speeds. But when you punch it...beware, sounds like thunder was unleashed from under your car!