PC speaker systems are definitely susceptable to RF interference, and house wiring can act as an antenna and bring RF into the system. I operate a Ham Radio station right next to a couple of my PCs and have had to RF-proof both systems. The first thing to do is to get some of the RF choke cores that Radio Shack sells. These are rectangular and are sold in packages of 2, I think. They have a plastic jacket that can be openned to make them easier to use. The package has instructions on using them, but the idea is simple. Each of the wires in your speaker system should be wound around at least 1 core. They are stackable. If you think that the RF is coming in on the power wire, be sure to use a couple on the wire from the wall wart to the subwoofer (assuming you have that kind of system). If the wire is stretched out, it is sometimes more effective to puts cores in more than 1 place on the wire. If you only want to put the core in one place, put it right at the back of the subwoofer, which will also contain the amplifier. Don't neglect the speker leads, especially if they are long. Any excess lead should be coiled tightly. Good luck.