I have the full Magnaflow system , there is a muffler just behind the rear cat and another one which looks like a muffler at the rear with two exit tips. I need to get rid of the dreaded drone and looking for advice, if I install a flowmaster will it restrict too much since my system has another muffler at the rear?.Or is the rear piece simply a resonator?any suggestions would be helpful. I also have a cat forward 2.5 inch system and stainless headers , sounds great but the drone is too much.?