I have a hum in my Onix Rocket RS1000 speakers. They are driven by a 7100 except for the powered woofer which has its own amp. The hum disappears when I turn off the internal amp. It also disappears when I disconnect the speakers from the 7100. The hum appears when I connect the 7100 to the high level inputs on my SVS PB12-Plus/2.

Any thoughts? Is this a known issue with the 7100?