I've just bought a plasma TV and it keeps making a hissing sound
Its only plugged into the cable box and no other electrical equipment, every couple of minutes it hisses for a few seconds and we can't figure out why. We tried plugging it into the DVD player and it does exactly the same. It has a sounds test on it and the sound is fine during that so wondering if its not a fault but is something we are doing. Any advice greatly appreciated! 

