I've already had my Grizz re-jetted due to the high altitude here in the southern Nevada mountains, with much success, Last week we were at 6,500ft. and it ran great, with lots of power, Now here,s my concern I would like to put on a high flow exhaust to get the full potential out of the 660 engine, However I do not want it much louder than the stock muffler that came with it, Is there such a thing as a quite high flow slip on? HMF, Pro Sound? any thoughts, suggestions, I hate the sound of a loud single cylinder machine, twin cylinder o-kay, but not the Grizz,,