I'm getting a very noticeable hum when I switch on my amps running both into the same stereo 4x12 cab. I'm running a Rivera Knucklehead on one side and a Soldano on the other side of a stereo 4x12 Rivera cab. When I have only one amp running and the other is in standby, there's no noise. But when I switch that second amp on, a loud humming appears on the first amp...it appears only when the second amp is on, whenever I put it on standby, the hum from the other amp goes away completely. I've removed the grounding from one of the amps' power plug so it's not a ground loop...I'm using a loop selector to switch between the two amps' inputs. If I disconnect the selector and play each amp separately (even with the other amp running idle) there's no humming at all... The cab I'm using has a metal plate where the jacks are mounted...and the loop selector is also metal: Could it be that the grounds from the two amps are causing the hum? Any help will be highly appreciated.