How to fix the annoying noise you hear when using the mouse/hdd. There may be more causes/fixes but the one that completely solved my problem on my Windows 7 x64 was muting the PC beep output. To do so:
1. open volume properties/playback devices
2. open the properties of your active speakers/output device
3. go to levels tab
4. make sure PC beep is muted.
HTH,
darqwan.