> Old ones maybe. Even the "quiet" new ones cause a problem when placed in the confined area between buildings[1]. It projects low frequency noise into the ne

> Old ones maybe. Even the "quiet" new ones cause a problem when placed in the confined area between buildings[1]. It projects low frequency noise into the neighboring structure. Very hard to deal with. You still need to be careful with placement[2]. [1] http://www.quiet.org/readings/a-c_sound%20advice.htm http://www.quiet.org/readings/a-c_sound%20advice.htm [2] https://www.eugene-or.gov/DocumentCenter/View/17196/Neighborly-Installation-of-Heat-Pumps https://www.eugene-or.gov/DocumentCenter/View/17196/Neighbor... (PDF)