I can't find the source for the life of me, but I remember reading an article about 6 months back that declared basically "there is not a single square foot of land inside the continental USA that is considered 'silent' any longer".
In other words, no matter where you "go to get away" in the USA, you will never truly leave the buzz of the city.
I just skimmed that paper very quickly, and it seems to include wind and water. If you count all the noises that nature makes, nowhere on the planet is going to be "silent".
In other words, no matter where you "go to get away" in the USA, you will never truly leave the buzz of the city.
EDIT: Perhaps this is it http://geohazards.usgs.gov/staffweb/mcnamara/PDFweb/McNamara...