>It's interesting that you didn't once mention the sound of humans.

I think they are implied by the din of the city which is the din of people even if it comes from a loud car, that loud car is loud because of a person. For the driver of that loud car being able to really hear the engine could mean the driver is the sort of person who wants to hear the engine and is the sort who can isolate each and every sound the engine makes telling them a great deal about how well it is or is not working. Or their engine might be about to fail and it is a constant reminder of another thing they need to figure out how to pay for and praying it holds out until next month when they get their Christmas bonus even if that means the kids will have not have much of a Christmas. Or it might just be that it is their way to block out the constant din of the city. Or they may just want the city know that they are there, that they exist. screaming to the heavens as it were.

All those sounds which make up the din of the city have meanings and are personal, they connect to a person and a life. But I did make a conscious decision between natural and unnatural noise, nature vs city, people are sort of a grey area there and getting into that would complicate my point. The person living out in middle of nowhere miles from anyone is generally allowed to make as much noise as they please unless you happen to be camping near their property, then they are probably going to be considered rude for disturbing the tranquility and your vacation from the city even though you are the one encroaching on their life, not the other way around. As far as you know no one lives within 100 miles of your campsite and here are all these noises which do not belong 100 miles from civilization.