Very much at my wits end here. This noise is driving me bonkers.

I have restarted, closed every program, run virus checks, trojan checks, malware, spyware checks, cleaned my registry, restarted, haven’t added any new hardware or software and I still cannot figure out where this noise is coming from. If the speakers are off, simple – no noise. The time in between the sound varies, sometimes it’s 2 seconds and other times it can be 10 minutes. It sounds like a CHING, cash register or photo snap noise. Happens even when I have nothing open and just there @ the desktop. I know I’m not back doored so nobody has my webcam open and is snapping photos or anything like that. Anybody have any clue as to what this annoying god awful noise is? I can’t listen to anything (videos, music, etc) because the noise adds itself right in there just to bug the crap out of me! There is no noise @ startup, & yahoo, aim or any other messenger is not open and the noise still goes on. HELP!
No screensaver running and it does it all the time no matter what is open or closed, program wise. i have run every anti spyware program out there well …almost and i have no clue where this noise comes from. Was hoping someone else had this happen and could give me an answer.