Sound Starts on Then Goes Off Randomly (by 2 users)

Hello.

I have a problem with my audio. When I start up my computer, sound works and everything is going good. Then, all of a sudden I'll play a random sound or I'll just be on my computer for a while and all of a sudden the sound goes out. But, instead of hearing nothing out of my speakers, I hear this muffled static sound coming out of the speakers. And, every time my hard drive starts to think harder and load, the static sound coming out of the speaker gets louder. I tried switching speakers but I had the same problem. I think it's an internal problem. I checked my sound card and every thing with the sound card is OK. So, since it's not the sound card, I don't know what it is. By the way, I am using a P4MBMS motherboard.

So, to sum up my problem and question: I start my computer each time and the sound is on. Then, all of a sudden I run some random sound or I have my computer on for a while and the sound shuts off but I hear a staticy sound. My sound card and my speakers aren't the problem. What can I do to make the sound stop randomly going off??

Please respond and thank you,
Tom