I was just leaning over my reciever to plug in a new cable, and when I touched one of the small screws on the side that holds the top on the chassie, I got a mild shock. Very mild, not really painful, but still. I know that's not normal, but what could be causing it? I've never had that problem before. The wiring in my house is really old, but could that cause the reciever to pick up a charge.