Sound Loss / System Slowdown

My system has recently developed an annoying problem which is causing me some concern as it could indicate something serious.Quite often when it boots up, there is instead of the properly functioning sound, a continuous high pitched whine. This goes away when I reboot. Sometimes though, this issue arises during games or other general use.If this happens when the system is running, not just the whining sound is there, but also any 3D or video graphics slow down a lot.I have attempted to remedy this by removing and replacing the soundcard and an uninstall/reinstall of the drivers. Unfortunately with no affect as regards removing the problem or it's cause.Outside of these times everything runs as it should and the sound functions perfectly both through the speakers and headphones connected via the front panel box supplied with this XF-fi series card.I am thinking about a full re-intallation of the O.S if nothing else works.