My speakers have started buzzing quite loudly. Before, you could only hear the buzz if you put your ear right next to the speaker but now it can be heard from the seating position (and I haven't changed anything). I've noticed that when I turn on my A/V receiver, the buzz is quite faint/quiet but as soon as I turn on my plasma TV, the buzzing gets a lot louder. The buzzing is not volume dependant. I have connected all of my equipment (plasma TV, A/V receiver, and DVD player) on an extension socket (where the extension socket connects to the power outlet and offers four more outlets for connection). Could my extension socket be the culprit? Should I try investing in a power conditioner?