I built a muffler for the Onan...and it didn't really matter.

[Dualfuel]

So I replaced the mushroom muffler on the Onan CCK with a home made muffer...I got the exhaust note very quiet. Turns out the valves or something are actually the nosiest things now. Still not an unpleasant noise, as much as just a bunch of clanking.

[Tom T]

I did the same thing on set up it sounded like it was coming apart from all the clattering.