Crackling Sound Problem on my Computer?

Hey all, I've had this problem with my computer lately where, after a certain amount of time, the sound will start to crackle and pop. This only happens every half hour, and when it happens, I just open up my audio control panel and switch it to a different setting and back, and everything is fine. This never happened when I had a USB headset, only when I have to plug into the jacks in the back. I'm not using a soundcard, just the Asus M2NSLI motherboard. Can anyone help me out?