I noticed today that there is a faint buzzing sound coming from all of my speakers. At first I thought something was wrong with both of my main speakers, but it is coming out of my surrounds as well. I had been running some subwoofer tests to set up my BFD when I first noticed. It is there even when the reciever is turned all the way down, and doesn't really seem to change volume with the reciever. However, with no source material, I can hear a fluttery sort of buzzing sound when I turn the reciever up. I have recently moved into a house with very old wiring, could that be my problem, or does it sound like something with the reciever, or maybe some sort of magnetic field? I really am lost. I haven't been listening to anything at really crazy levels or anything. I'll be trying a friend's reciever this weekend, but until then, any suggestions on what it might be or how to fix it?