I also have the same problem but it only started happening recently.
System specs are in profile I think...
Anyway, so far I've tried uninstalling my Creative X-FI Titanium fatality pro and enabling onboard from my mobo (Gigabyte P55A-UD4P) and it was exactly the same...
So I thought it might be my headphones?
Newegg.com, new headphones = SAME PROBLEM...
So, looking at the variables, it seems the WIN 7 INSTALL has somehow gone sour? It was ok originally, no new
drivers have been installed. The only thing installed has been windows UPDATES... Could this be the culprit?
My next step (as much as I hate to) is to do an entire new install of Windows 7.
If that fails, I'll go BACK to XP and see if the problems still exists. Pain in the hiney but I seriously feel it's a Windows 7 issue and would like to prove it. It's an obvious issue with Windows 7....look how easy it is to find posts where people are having the same issue. LOTS of people.