This is a very weird problem indeed.
Windows 7 system makes noticeable buzzing noise in the speakers whenever certain apps are open.I have noticed this problem at least with all browsers and Filezilla.
Searched around for a solution but so far have no any clues...
I don't think that's your operating system. More like your motherboard/hardware. If it's a sound, you can simply turn them off at the Control Panel -> Sounds.
(But I highly doubt it's a Windows 7 sound..)