Maybe it's reversed in US, but I find the exact opposite here in UK - a house from 1930s will offer much better sound insulation that any new build with its cardboard-thin walls separating properties.
Definitely my experience in the U.S. also. Buildings are built to meet minimum code, including the amount of sound allowed to pass through walls between units. Minimum code is nowhere near good enough to block any amplified music/sound, much less if you're unfortunate enough to share a wall/floor/ceiling with a neighbor with a powerful subwoofer.
It depends heavily on a property. I rented a room in a fancy new build flat for a while and the only way I knew the neighbors existed was when I met them in an elevator.
