[bendhoefs]

In my experience it's newer buildings that tend to have paper thin walls. In my current apartment(late 70s) I very rarely hear my neighbors.

At my last apartment I could literally hear my neighbors cough. Absolutely miserable. I wish there were some sort of measurable standard rating for noise transmittance through walls that landlords are obligated to disclose to potential renters.

[Gigachad]

New buildings have strict fire separation requirements that pretty much enforces sound proofing. All new build high rises I have stayed in have had total silence.

[jalk]

Seen many buildings where the concrete walls soundproof the rooms but plumbing ducts in bathrooms transmit sound like crazy - as in you can hear conversations from people several floors down. The inspection hatch cover made of thin sheet metal seems to act like a microphone exciting the air in the duct causing the other covers to act like speakers