On one of our camping trips last year our next-spot neighbor had one of those wee-bitty Hondas that he was using to charge the house batteries in his travel trailer. He ran it from around 9 a.m. to lunchtime each day- plugged it in and sort of shoved it under the trailer. I only knew because I saw him do it; I couldn't hear it over the noise of the river, the kids playing and my wife listening to (low-level) music via her zune/sirius boombox. I didn't smell it either.
In contrast, my step-dad, on the other side of us fired up the 80's era Onan gennie in his motor home in the afternoon and basically drowned out the world, and it stank. I mentioned to him at one point that he might consider doing himself and the world a favor and upgrading to something more modern and he got a little defensive, but that's the way that goes. Sometimes a 'seed planted' is sufficient; they're considering getting rid of the behemoth altogether and getting something from this century.
The point is, the little Honda wasn't bad at all from maybe 30-40 ft. away.

Cya,
Robert

--snip--
No sir -- I'm sticking to my generators make poor campground neighbors
stance until someone demonstrates otherwise. In a quiet campground. Like
White Tank CG in Joshua Tree, or Laguna CG (on a weekday) near San Diego.
Places where you can hear a car coming long before you see it.
--snip--