I need help from you guys.

I think my PC is recently infected with spyware or virus.
The situation is once a while, pop up comes up BUT only audio but no visible new window will be open.
This audio ad will continue somewhere between few min to over five min.

I ran "adaware 2008," "Norton Virus" and "Spyware Docotr," but none of them helpe to remove this situation.
just in case, I also remove all internet cash, and ran window cleanup, defrag, error check.

so now, I ran out of my idea.
so what can I do next? please help me with your knowledge!!

Thanks