When I press the 'mute'-button (on windows GUI or on my logitech keyboard) I can hear a short beep through my speakers. The volume depends only on the volume settings of the speakers, not the windows settings. This happens on the front and back jack plug... with my head phones as well. (So it's not about the speakers.)
Strange thing, i had the same problem with my previous PC, but back than it was more like a crackle (like when you plug in speakers that are already turned on).
Is it possible that my speakers may be broken and kind of destroying my sound card? Has some one an idea what this could be about?