Possible sound issue, but not sure.

Not strictly game related, however this only seems to manifest it's self when this game is running. But not always.

My system has recently developed an annoying problem which is causing me some concern as it could indicate something serious.
The machine can be running normally everything working as it should, then suddenly the sound cuts out and is replaced by a continuous high pitched whine through the speakers and a slow down of any web streams running at the time although the game still runs normally except for the sound. This goes away when I reboot.

Have replaced the memory sticks, sound-card and the hard drive. No luck. The issue went away for most of a day then just returned this evening whilst playing this game. No idea what else it could be, the only things left I could replace are the cpu, graphics cards and of course the mainboard. No budget for those at the moment.

System:

OS Windows 7 HP 64 Bit
CPU AMD Phenom II X4 3.20 Ghz Black Edition (o.c to 3808)
Motherboard Asus Crosshair III
Memory X8 Gb Corsair Vengeance (X2 4 Gb sticks) 1600 (O.C)
Graphics Card X2 Sapphire HD 5850 Toxic PCIe in X-Fire
Sound Card XFi Champion series with front panel box
Monitor(s) Displays LG W2361 - 23 inches (1920-1080)
Screen Resolution 1920x1080
Keyboard Logitec G19
Mouse Razer Diamondback
PSU Thermaltake ToughPower 700w
Case Zalman GS1200
Cooling Corsair CWCH80 Hydro Series H80
Hard Drives 300Gb Velociraptor Western Digital SATA II 640 Gb Western Digital SATA II 1TB


Getting really annoyed with this. I may as well have bought a new machine, which in a slow way seems to be what I am doing.