I bought some new speakers, Logitec z533. Plugged them in no problems, except there is always a white noise coming from the speakers. Even when the computer is turned off and even if they're not plugged into the computer at all. If I just plug in the sub woofer so that it has power and plug the speakers into that, nothing else plugged in at all, they emit a slight white noise. When I turn the speaker off by turning the volume down until I hear a click, then the sound goes away. The noise as far as I can tell doesn't get louder as I turn up the volume. I have no idea what's causing this problem, I've updated, cleaned, scanned, and everything. It's not my computer, its something to do with the speakers themselves, I've had this exact problem before with another set of speaker so got from a friend, however I dismissed it thinking they were just bad. Am I not doing something right?