I recently installed the fast intentions catback. The member I had bought it from had cut the resonators in the x-pipe off and I installed it unresonated at first. Without the resonators, this catback drones really bad even for someone that is used to loud cars.
So I had the resonators that were included welded back in and the tone is pretty much exactly the same, it's just about 15% quieter. This video was before I put the resonators back in.