Urban environments can often be less noisy than suburbs next to highways/freeways; due to extensive use of subway infrastructure - which moves the associated noise underground. Also, a suburban commuter spends a lot of time in a car commuting, being subjected to the very noise the parent poster is referring to.
I think that's the more minor part of the noise that the original comment was referring to. It's much easier to insulate one's detached house from suburban noise than it is to insulate one's apartment from noisy neighbors on the other side of a shared wall. It's also my experience that those noisy neighbors are a much bigger nuisance than the traffic noise in the first place.
On a tangential note, I'd be curious to know whether you have any links to back up the claim that urban environments are often less noisy. I don't disbelieve the claim outright, but it sure doesn't match my personal experience.
I was replying specifically to the "in another you hear BUMP BUMP BUMP every 2 minutes" comment which seems to imply that trains must be above ground. In Manhattan, NYC you can hear the subway from the street and the noise pollution is awful (eg. ear-piercing sirens and traffic noise at all times), but it's not like that everywhere else.
I'm writing this from the 11th floor apartment in an apartment town suburb 30 minutes by subway from Seoul. It is dead silent. Very little traffic, and everything is walking distance. From above ground you don't hear the subway at all. Sound insulation in this apartment is pretty good so I never hear my neighbors (actually there's only 2 apartment units on each floor).