I was just having this same problem while trying to study (listening to reading lectures, so it was very annoying)
I am using on board sound, but noticed in Device Manager it was using the standard Windows/Microsoft HD audio bus. I installed the drivers and it was still the same.
I then Uninstalled the device entirely from Device Manager, and then allowed Windows to re-discover the device.
Amazingly the problems are gone, sounds fine now!
This is Windows 7 Enterprise x86. I have x64 at home and the same problem (pretty much same hardware) and will be attempting the same fix there later tonight.
Try blowing the device away in Device Manager under Sound, Video and Game Controllers, and then doing a 'Scan for Hardware Change' and see if the problem corrects itself.
worked for me