Each branch has its own breaker.

Maybe you should try adding a blender. The emissions from the blender may destructively interfere with the sub noise \:D .

If it makes you feel any better, I have a slight hum with my 600 but it never interferes with listening. As a matter of fact, no one notices it unless I point it out to them.

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