Espar gas cabin heater
Just to clarify, I don't find the noise of the Espar INSIDE to be much of an issue. It's the noise outside coming from the exhaust that is noticeable. When the unit is running, it sounds like a (quiet) jet engine. Also, when it starts up, it has a distinct cranking rhythm, sort of like an old, hand-cranked siren (not the siren sound, but the rhythm).
Search for Espar+muffler under author:Scatter on this forum. He installed a muffler on his and says it works very well. I just haven't found the time to do it myself.
2008 E350 EB, V10, GTRV Conversion