No, not the fans. It's the magnetics.
"Why do transformers hum?"
"Because they don't know the words...."
Sorry about that. :) The Xantrex Prosine 2.0 that I have had would start up the fans under a load, and sometimes inexplicably in the night. It was silent but for that. I have a large Mastervolt on the boat, it will start the fans with a good load too, but otherwise silent. This Magnum buzzes as soon as you turn the inverter on, even with no load. With a load, it is quite loud in my opinion. Magnum tech support says "that's normal, can't be avoided". Except at Mastervolt and Xantrex I guess?
