I guess I'm one of those who nudged the discussion off track. But many of us are involved in this now, so let me add a few more observations:
We had an old BFA (the "4KW RV Genset" of years ago. Two-Cylinder with no sound box around it. I'm sure it put out more dbA than our current MicroQuiet 4KY, but the sound was not as annoying. Yes, it was a Twin as mentioned above, but it was also an 1800RPM unit so it didn't sound as "busy" as the 4KY which is 3600RPM. I think it needed engine mounts. Rattled dishes in the cabinets but its tone was pleasant. Like a garden tractor locked in a closet.
We used a friend's truck camper with a MicroLite 2800 LPG in it and I was amazed how quiet it was. It was out beyond the rear bumper (the part of the TC not inside the truck bed). Inside it sounded about like the microwave running and easy to talk over outside. But then, the TC was a BigFoot...
I find our 4KY acceptably quiet given that I'm the one benefiting from it running. But I don't run it any more than I have to, and make it a point to use StaBil in the fuel and exercise it often.