What are your system specs? Make and model #. If you have an add-in audio card, what is it.
Was there something that changed on the computer right before this happened? Windows update, new graphics card, any other add-in card.
One thing to try in situations like this is to re-install your audio drivers. Best to use the latest ones from your pc/audio card manufacturer. If you don't know than we can help if you post your system specs.
Might also be worthwhile to find out what your voltages are from your power supply. Best way is to go into BIOS and record from there. Let it sit for awhile (5-10 minutes) and see if you are getting any fluctuations. Post back here what those are so we can rule out your psu (or not as the case may be