Noise pollution in the city is just a fact of the population density. Speaking from experience, if you've lived there for some time your hearing won't even be sensitive enough to truly appreciate the difference in a rural area.
It's just never going to be <35db in the city like it is in the rural community that I live in where I get to wake up to bird song. It took me 3 weeks when I moved back from living in the bay area to "hear" how quite it was, years of living in the city had desensitized my hearing. Sure, cars and especially fast moving cars contribute to the din of the city, but considering how loud it was even when the streets were empty in the middle of the night, I think that HVAC, elevators, and subways along with people being people create plenty of noise.
In the rural area I live in I can hear a car coming down the road from over a mile away at night, even with terrain in the way, and because of the low density most of the time throughout the night there are no cars. There is just no way you are going to be able to attain that level of quite with urban population densities - the 24/7 public transit would be louder.