It is usually some pipe, a Muffler with a single 3" inlet and dual 2.5" outlets for dual tailpipes. My Magnaflow doesn't drone. It is a bit loud when towing 7500lbs under heavy acceleration. Normal driving, you can talk normally and hear the radio fine.

You will gain the most from the Diablosport Predator #U7137. 20 RWHP and better mileage ad well. Not much gain on the intake and none from a TB spacer. The exhaust will pick it up a little bit as well.

 

Flowmasters drone pretty badly, and rob the Hemi of power. If you want a good rumble, but a moderate loud tone that won't **** off the neighbors, go for a Magnaflow or Aeroturbine, and if you don't care about pissing off the neighbors, well, Cherry Bomb is the way to go. Also, any exhaust shop will be able to fab up any exhaust setup you want, and generally cheaper than buying a catback kit.