I've spread them out as far as possible, almost touching my 80's and the hum is still there. It is not real loud, but when everything is quiet I can hear it 12ft away. So whether they are right below the center touching, or 8ft apart, still have the hum, unless I turn one or both of them off.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85