Quiet spots are harder to find, but there are quite a few. Free, dispersed and quiet? Needle in a haystack.
That goes with high population density and a dearth of public land.
Of course that map also reflect population density. Industry, cars. But in less populated areas there are sometimes strip mining operations which can also be VERY NOISY with blasting and machines. As can military bases with planes flying in and out doing training exercises and munitions testing ranges too. Camping anywhere near a rifle range will also drive you bonkers in the daytime. Or just camping near other campers. A flock of wild geese is pretty noisy as well but at least they go to bed when the sun goes down instead of staying up and partying.
It's interesting that some rural parts of north Texas and the midwest are so loud. Sound travels farther with no geological features to stop it, I guess?
And let's not forget humidity. Been to Oklahoma lately?