Plug it into a different outlet see if it changes. Are you using a power conditioner of any type? If no, try one. If you think it is receiver related when the unit is off try
disconnecting the interconnect to the sub and see if it does it. If it still does it is something in the A/C line
disconnecting the interconnect to the sub and see if it does it. If it still does it is something in the A/C line