The Onan 4K in our small Class C is pretty quiet - due entirely to how Winnebago installed it.
There's heavy padded carpeting on the floor over the Onan - so we can leave it running and get by just fine inside for as many hours as necessary. We even have left it running at night while we were drycamp sleeping in the extreme heat and humidity of the Southern U.S. in the summer.
Winnebago mounted it in the external cabinet up high so the whole unit is up inside - not with it's bottom hanging down low enough so it can be seen from the outside like others I've seen in Class C motorhomes - which then makes the Onan louder from the outside.
I have listened to our Onan A LOT from outside at all angles and distances. To me, camping next to it would be tolerable ... especially when our motorhome is parked on a surface that doesn't reflect sound well - like grass or dirt. It could be quieted even more from the outside by gluing sound-proofing material onto the cabinet's interior walls facing the generator.
Most of our Onan's sound is from it's cooling fan, as I would expect it should be from a $3000 generator intended for full power use even in high temperature extremes - like boondock camping in Death Valley, which we have done.
2005 E450 Itasca 24V Class C
