There is a company that makes a "stealth muffler", it is an add on additional muffler that makes them more quiet, also reduces performance just a little. I would guess any small muffler with the right diameters of intake and out exhaust would work. The just become an extension of the original muffler. The "stealth system" just runs sideways left to right added on behind the factory muffler. Compared to other machines I have been with I found the Kymco to be quieter than most, not sure just how quiet you need.