First, the housing stock is old. It’s hard to build new, mostly for zoning reasons. Old building will be more leaky and creaky.
Unlike most of the country, even new construction does not include central air, and often does not include central heating. They use wall units called PTACs, even in “luxury” buildings. These units are loud.
NYC is dense, which means each neighbor’s noise matters more, including our automotive “neighbors”.
That said, sirens are far and away the biggest problem. They are loud enough to distort in one’s own ears. Well over 100db at street level. Apartments are close to the street. And clogged streets means emergency vehicles move slowly, while screaming.
Reducing this outlier would be the single biggest win, even over car traffic, which is comparatively benign.