I'm with you on this, I detest the sound of generators when I'm camping. For that reason I usually stick to the non-generator campgrounds in Yellowstone. Even though they aren't reservable, they really aren't that tough to get into
Madison Campground has a tent-only loop. It's is set well away from the RV section and spots ARE reservable. I'm not sure if generators are specifically prohibited there - you can call and check - but during the couple times I stayed there no one was using a generator.
Edit: The tent-only loops are really much nicer than the RV loops (where tents are also allowed) at Madison. Request loop H to be furthest away from the RV section.
Madison Campground map.
