It is no secret that many complain that they hear how their computer works when using the sound built into the motherboard. You can hear the mouse moving, the pages scrolling, the worms crawling on the hard drive ... :) Disabling various inputs of the sound card (LineIn, Microphone, CD In) does not help or helps but not completely. Recently, I ran into this problem on as many as 2 computers for which I listen to music. Solution for XP and Windows 7 under the cut.
As it turned out the fault is included in the PC Speaker mixer. True, for some reason, it is called PC Beep, but it doesn't matter ...
WinXP: Go to the mixer

Parameters -> Properties find in the list of outputs PC Beep, put a daw

Click OK and see the noise source in the mixer. Turn off and enjoy the silence!
Windows 7: Control Panel -> Sound
In the Properties of the Speakers we chop off the unfortunate PC Beep
