they are inverter gennies, like the Honda 2000, only (a lot) bigger) on minimal load, they are barely turning over, just a light purr...
And they are made for motorhomes, and quiet is a major design item.
Loaded with the 100 amp battery charger and a pair of roof a/c's, they can be heard pretty well.
My nascar buddy runs a kippur 3500. He runs it all night, he uses a cpac, and his converted bluebird schoolbus doesn't have an inverter or much of a battery bank... And the kippur is quiet, it is a Chinese Honda clone.
Those champs and other open frame "construction crew" gennies, they do not belong anywhere near any RVers, that is just not what they are made for.