Found out my 1970s building has zero sound insulation, just two sheets of drywall
A retired contractor who lives on the 3rd floor here in Portland showed me a cutaway photo of our exact building type, and it turns out there is nothing between units but a 2 inch gap and some wire. He said the whole complex went up in 1974 using the cheapest materials going, which explains why I hear my neighbor's microwave beep. I always figured old buildings were built like tanks, but apparently thin walls have been a thing way longer than I thought. Has anyone actually had luck adding mass to a shared wall without tearing everything out?