It has nothing to do with your s-video cable it is a ground loop hum probably related to cable television. I'm assuming you have cable tv, if so get a cheater plug from any hardware plug to check, if the hum disapears when the ground is lifted you've found your problem. There are other safer alternatives to cheater plugs to pursue as a long term solution, I can't think of any off hand but perhaps someone more knowledgable will chime in. If not just do a forum search using the word hum and you'll find a wealth of information. Good luck!
