Sound problems

When I play any game or listen to music, souds work few minutes, and suddendly the only noise I can hear from the speakers is the f***ing howling. If I want to hear sounds again, I have to restart my computer, and then the sounds work again few minutes… Does anybody know what is the problem, and how can I fix it? The speakers aren’t the problem. I think the AC97-integrated soundcard is broken (I’m not sure). I have Microstar MS-6340 motherboard.