Mostly quiet, except when suddenly started. I'm not happy with the fact that it says pure sine, but the literature that comes with it says it doesn't register as pure sine on sensitive equipment, and has a list of obsolete equipment. So it was really disappointing. I would also like a wireless remote control, that would be better. It can be max 5000W because it doesn't drive a 220V 7.5A supercharged motor as well as a normal light load. The compressor has a very high starting load/torque but will not start.