I have speakers in zone 2 and a denon avr-2311ci. Sonance speakers are hooked up to the zone 2. Even when zone 2 is turned off on the denon, when the volume on the wall control for the speaker is turned up, it hums slightly. Do you know why that is? In order to shut it off I have to turn down the volume on the wall controls in each room.

Any help would be appreciated!