My next door neighbor is a 50 unit or more, 6 story apartment building. Their roughly 10-15 ft tall HVAC is situated at the edge of the rooftop closest to me. When it kicks on, my wife and I can hear it even with the back doors and windows closed. Open window sleeping, even with earplugs, doesn't work well. In addition to the noise coming directly into our apartment, it bounces off two flat surfaces from other neighboring apartments, making it even louder.
Another neighbor has approached the manager onsite about installing baffles or other soundproofing but they said it would cost over $10,000 and therefore refused to do anything except tune up the unit. They have been, shall we say, difficult to deal with. I find the $10k price tag hard to believe. Are there recommendations for alternative approaches or places I can go to get an estimate without direct access to the unit?