When I have been in NYC recently, it's seemed remarkably quiet to me. In particular, I don't see many cars.
(Only the subway is loud. But that doesn't stress me out, because I don't have to do anything. You get on, you let your mind wander, you get off, you take a little walk.)
When I was a child, I saw movies set in New York, and the streets were always choked with traffic. The sound of a car horn was almost a shorthand for the city. You'd hear it in music. They'd use it in establishing shots in films. Always yellow cabs.
Even a decade or two ago, you'd stand, as a pedestrian, at the crosswalk, waiting for the light to change.
Now, often you look both ways and the street is clear for a whole block. You don't wait, you just cross.
Sure, there's a rhythm to it. Even decades ago, the Financial District, choked during rush hour, was spookily-empty on the weekends. So maybe I have more recently walked around in the places and times that are at the troughs of that rhythm.
But I suspect there is also a longer-term trend, or perhaps a step change, caused by COVID: Cities just seem quieter now.
To an extent it is good. I'm happy to see a city by for and of people, rather than ditto for cars, their manufacturers, and their buyers (who lack alternatives). By all means, let restaurants build decks on the street; decorate them with flower boxes; let people meet there for brunch or after work.
There is also a negative aspect. There is still, I think, a suburban hangover. I see this in friends who it is now difficult to drag out of their apartments and away from their video games; in other people who one might frustratedly describe as "suburban women voters" who, in rare acts of personal courage, mask up and use the subway (they stand out from the people who actually live and work in the city. ... I shouldn't mock them; at least by seeing the reality they will overcome their fears); and in the rhetoric of the political Right, which seems more grounded in Escape from New York than in reality.
So I suppose several forces have made the city quieter. Some positive, some negative. And popular perception lags (as it must; this is the nature of information transmission).
Apparently the surge tolls they implemented recently contributed to less traffic, in Manhattan at least
The loudness of cities is generally a product of cars.
Very busy areas of cities without many cars are fairly quiet.
Tire noise, exhaust noise, horns, etc all make a ton of noise. Living near a highway in the suburbs is probably inherently more noisy than many cities.
I like to think about the time around 1900 when the population was far far higher than today, but there were no cars. Horses don’t make the same noise.
Of course there was heavy industry in that day so that would be loud and filthy.
How quiet was dense NYC in 1830 though?
I guess it would depend on where you were. If you're in a high traffic area full of horses wearing metal shoes stepping on cobble stones and handcarts with metal rims rolling over cobble stones, it could probably get pretty loud.
I bet it could get pretty quiet, even with the density.
College campuses are often pretty dense but also pretty quiet.
I had the same experience being in downtown SF (near Market) for the first time in a few years, but I attributed it to the number of electric cars.
The whole visit felt weird, and eerie, and off somehow, but I couldn't figure out what it was. And then I was standing waiting for a crossing light and heard the clicking of a scooter's turn signal ~20 feet away. It stood out because it took a few seconds to realize that I shouldn't be hearing it because of other noise.