Dang. That really sucks.

I recall you have a lot of devices like a ps3, Xbox, etc. Try disconnecting all those from the Denon and see if the problem goes away.

Try plugging the ADA into the same receptacle as the Denon.

Also make sure you're not picking up radiated noise on your RCA cables, power cables or power cords. Try wiggling those around to see if it gets louder or quieter.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated