The most common cause of this is a dimmer somewhere in the house. Try turning all dimmable lights off completely, regardless of where they are in the house. Unplug all automatic night-lights. If the buzz stops, turn the lights back on one by one to find the one affecting the power line, and replace it with one that doesn't. Please contact your local home theater retailer/installer for more info on electronic dimmers that are suitable for home theater (even with remote control!).