it's the transformer that makes that noise.and the trigger setup doesn't get rid of the problem.It's a pretty normal situation that transformers sometimes creat a huming noise.And it's not through the speakers...I have 7 m-200.When i power them up, no humming, but if i let them into standby for a long period, some humming can occur.I also own a avr8000 and the toroidal transformer sometimes hum too when on standby mode for an extended period.The situation occurs with both toroidal and E transformers...Sometimes, when i power up my 2 pa2000, they produce a small transformer hum.If i power them off and on again, it can make the hum go away.

anyway, i read somewhere that thighting the both that holds the toroidal transformer can reduce vibration causing the humming.I know i wouldn't tough a thing.If you can ear that kind of hum while listening to your system, just crank the volume louder.