Try the speakers in a TV or other PC see if it still makes that sound......Try reinstalling your sound card drivers.
I have a double knocking sound coming through my speaker every so often, more oftern than not. The sound emits whether computer is in use or not. I have no viruses or spyware on the computer as I scan chronically. I am wondering if anyone can tell me how to rid my system of this noise and if this is a signal of some problem in my system.
Thanks in Advance