neighbor-to-neighbor noise

Yes.

Also, ask them to confirm the names and phone numbers of all the general contractors who built each building. I'm sure the brokers will have time for all of this.

I'll give you a big tip that solves a lot of problems in apartment living:

Look for a doorman building that allows dogs of any size, and actually has big dogs.

I've yet to visit a building with poor soundproofing that allows big dogs.

go see the apartment on a weekday evening...that should tell you everything you need to know.

i have a neighbor who regularly puts notes under everyone's door about not smoking, not making any noise because she has two children...sometimes an apartment in manhattan is not going to work and you need to move to a house in the country.

date of construction doesn't mean much. i see new devs built today which are almost perfect in terms of soundproofing, and others which are joke. it totally depends on the developer.

through the floor/ceiling noise is usually more of an issue. keep in mind that a poured concrete floor over a steel deck will transmit plenty of sound if there is no insulation, gaps, carpet or other sound absorbing layer above or below it.

we hear about people who move into a concrete building who are shocked by how much they hear. it's not the voices and dog barking sounds, but it is footsteps, tapping, kids playing and banging, etc.

visiting the place during a weekday evening is great advice. you should also ask the super about the frequency of noise complaints

I've looked very carefully at this issue in several new construction buildings in wmburg, and had extensive discussions with a contractor who retrofits old and new apartments to insulate from all kinds of sounds from adjacent elevators, to footfall, to loud side neighbors.

Basically, the construction has to provide some kind of insulation that interrupts the transferal of sound.

In these new buildings the ceilings are all 8 inch concrete with some sheet rock below to form the ceiling. He told me right off that "concrete is a good sound transmitter". Unless there is some kind of sound insulation mat between the wood and concrete (or unless they did a very good insulation job between the concrete and the sheetrock ceiling) you may not hear voices through the floor but sharp sounds like high heels would be very audible, some footfall will be audible, and maybe other household sounds. That's a huge issue for me.

Walls between units need some serious thought because simple sheet rock and insulation simply do not muffle sound sufficiently. There are special types of insulation, some places have concrete between unit walls (again, that alone is not key).

For retrofitting they build new layers of wall or ceiling and use special insulation materials which they say are extremely effective. It costs roughly 30psf.

In wmburg bad examples can be seen at w11, good examples at70 berry or i think 125 north 10th, and i suspect 80 met.