There really are 3 levels of generators being talked about here:
1, Open frame contractor generators, they are cheap, typically have a 500-700 hour service life before needing a new lawnmower style engine and run at a fixed speed of 3600 rpm. And are about as pleasant to be around as the neighbors teenage son's hotrod with no muffler at 3 am.
2, Onan RV generators, modern versions of these are usually enclosed in a fiberglass box and are mounted inboard under an RV, the RV body and the generator enclosure along with a real muffler, help the noise issue, though they can still give off a fair amount of sound and run at a fixed speed, 3600 rpm for the smaller units up to 4000 watts, with lower speeds, typically 1800 rpm for the larger units though some have reduction belt drives and run at 2800 or so rpm. The 3600 rpm Onans typically have a 1,500 -2,000 hour service life, and the lower speed ones have even higher with proper maintenance.
3, Inverter generators, these are the most fuel efficient, usually the lightest for a given output, and the quietest, they are also by far the most expensive for a given output when comparing quality brands, like Yamaha or Honda (see the Honda EU series for examples like the EU3000is or the EU7000is (the biggest of the honda inverter units, with a price tag to match at almost $4,500)
