Let's clarify something. Flowmasters technical department, and the people who manufacture and test their systems are 2 very different sets of people. The people who do the testing are not the ones you talk to on the phone. The ones you spoke to are sitting in front of a computer in a room full of cubicles, who type keywords from your problem, i.e. "loud" "bad fit", etc, then read you the answer that comes up. The ones who test the stuff (if they were reachable by phone,) I'm sure would (off the record,) admit that there is a sound change with nearly all mufflers, for whatever reason.