Strange intermittent gulping sound

Question

For some weeks now I hear intermittently a strange sound coming from my speakers. It lasts about a second, and because of this and also because it comes at random moments, I cannot make a recording of it so I will try to describe it.
It starts as a twittering sound, like small birds. and then below this sustained sound, and very low pitched come three gulping sounds, like bubbles under water, in a rising cadence. It is musical in the way the startup chime is musical and is in fact quite pleasing to the ear. It can be heard about every forty minutes or so more or less. It only disturbs me because I don't know what it means and I don't know where it comes from. I am concerned that it may be some kind of malware but if it is, it appears to be mischievous rather than malicious.
Now. It is not a mechanical sound. It has been digitally created of that I am sure. It is loud when my speakers are turned up and soft when they are turned down. I have closed all my running programs but it still comes. It is there when the computer sleeps. I have checked all preferences of all applications noting particularly warning or alerts therein without result. In particular I have checked Mail to see if an E-mail comes in at the same time, but there is no correspondence. It is not the "submarine" sound of mail's incoming traffic alert although there are some similarities in timbre. Nothing in Systems Preferences seem to cause it. I have turned off all in "Universal Access". It is not any of the supplied sound effects of the "Sound" Preference pane and I turned off "Play user interface sound effects".
I have kept my console open and checked it when the sound comes but nothing happens on the console. I re-installed and re-updated Snow Leopard. Still there. Have done Google searches and ploughed through discussion groups innumerable. Nothing. I use iAntvirus which has never detected any malware. If you notice hair falling out of your computer when you open this topic -it is mine!
The following is the list from my applications folder as this may help. In addition is a program called Surplus Meter which resides on my Dock and is always open.
ABBYY FineReader 5 Sprint
Address Book
Adobe Reader 9_
AppleScript Editor
Automator
Backup
Calculator
Canon Utilities
Chess
CleanMyMac
Comic Life Magiq
Dashboard
Dictionary
DivX
DivX Converter
Dupin
DVD Player
EPSON
EPSON Perfection 3490P_3590P
EPSON Scan
Firefox
Flip4Mac
Font Book
Front Row
Google Earth
Hardware Monitor
iAntiVirus
iCal
iChat
iGetter 2.7.5
iKeyV2.3.4
Image Capture
iSync
iTunes
Mail
Miro
Photo Booth
Preview
QuickTime Player
Safari
Skype
Stickies
System Preferences
TextEdit
Time Machine
Utilities
Wireshark
xvidcodec-r58
It's a puzzlement!
And I would appreciate your help if you can and will give it.
Many thanks. Plazatoro

Answer 1

Thank you Musicwind95, Bee and Mike for your prompt replies and helpful suggestions.
Mike it is not a sound from the Skype sound alert menu. These are all single notes whereas my "Deus ex machina" is polysyllabic and contains several notes. Musicwind95 - I didn't realize one could do that with quicktime x. You opened up a whole new world to me. I patiently recorded for two hours without the sound coming up, and indeed I haven't heard the thing all day. It's like the annoying rattle in your car which disappears the moment you drive into the mechanic's workshop! Now I don't know which is more frustrating: hearing the thing or not hearing it. Particularly as I would really have liked you all to have heard it - I think you would have found it interesting. I have been pondering why it chose to stop playing at this moment for I can't remember doing anything in particular except post the phenomenon into this discussion group and it would be weird indeed if that is why it stopped!
So. If it does return I'll endeavour to record it post it to u tube and resume this discussion.
In the meantime thanks once again to you
Len