The Billy Boat and most aftermarket systems replace the resonator with straight pipe. The picture that the guy above is thinking of removing is the catalytic converter

I just put on the Billy Boat performance system. It is very quiet, no drone, and just gives the Hummer a little rumble sound.

 

I did it on an Alpha and heard nothing different with regards to sound, no codes either, not really worth it. I did a cat back GM performance exhaust last year and that has a nice sound but not to loud. Actually getting better sounding the longer I have it on.