Try www.blastinbobs.com . I was running super 40 flows w/no resos on my 08 R/T,way too much interior noise at 75-80 mph on long drives. I rcently added a set of blastin bobs glass pack resos w/4" tips,still sounds good, nice rumble at idle, Bad A** at WOT and more wife friendly now. The center suitcase muffler on your 300 might be a straight through one(depends on the year),by removing / replacing the factory resos(at the rear of the car) it will be louder/more agressive sounding.Its also way cheaper than a full cat back ,D.