I have gotten tired of everyone at my club complaining about the noise of mine ( I am one of 2 guys with gas engines ) so this is the muffler I just bought from J'Tec. I haven't tried it yet but it has to be quiet. I spoke to a guy one time that had the Slimline muffler on a Brison 2.4 and he swapped it for a Bisson. He claimed he picked up 500 rpm's put on a larger prop and found it also quieter. I think part of the reason it is so noisey is that the clyinder part of the muffler is so small. The one I bought from J'tec is almost twice the size plus it has the 2 after mufflers on it.

Here's the J'tec