I removed the OEM center box (Resonator) and replaced with Forum X pipes. I noticed no particular increase in noise, but the X pipe did alter the tone. Last month I fitted Larini back boxes, but when I get home in a weeks time I am going to refit the OEM center box. Dont forget the center box is not a muffler its a resonator, and the purpose of a resonator is to eliminate unwanted resonance at particular RPM, better known as as exhaust drone.