I have some sort of computer virus that makes my computer laugh "wa ha ha ha ha ha ha" at me... How to remove?

No virus or spyware shows up when I run Norton Anti Virus or Spybot Search and Destroy but still every once in a while the laugh comes out of my computer speakers. It sounds like a jerky boy kind of man's voice saying "wa ha ha ha ha ha ha" and then it goes silent again. Also another variant is the... show more No virus or spyware shows up when I run Norton Anti Virus or Spybot Search and Destroy but still every once in a while the laugh comes out of my computer speakers. It sounds like a jerky boy kind of man's voice saying "wa ha ha ha ha ha ha" and then it goes silent again. Also another variant is the sound of a tropical bird cackling, like "ca ca ca ca ca ca." So far this is just an annoyance, but it's disconcerting nonetheless. Any help would be very much appreciated and I would be more than willing to PayPal you a few bucks to buy you a few beers if you can help me remove this problem permanently. I say permanently because I had the problem on my old computer and now it has shown up on my new computer. I used an external hard drive to transfer files from old to new so now maybe my external hard drive also has the virus?? Thanks for your assistance!
Update: Thanks, folks, for the replies. How do I post the processes list? When I Ctrl+alt+delete and review the list in Task Manager it is really long and I don't know how to copy and paste it here. I know that's a novice question, but please let me know and I'll post. Thanks!
Update 2: Thanks again for the info... I just switched to Panda anti virus and have run it and it did detect some additional spyware that Norton didn't detect... and the laugh has not come back recently. I also disabled buddy sounds on my instant messenger. We'll see. Thanks a lot! :)
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