OS X :: Screen Capture Sound Occurring Every 30 Seconds - Can't Turn It Off

Last week in the middle of my work day nothing special, the system started playing the camera shutter / screen capture. I started timing between the shutter, every 30 seconds, very annoying - the camera shutter sound - same as the shift-4 screen capture sound and same as the sound that occurs when you press the back button in terminal. I have a 15 inch mac book pro. 2009 model.

I wondered whether someone had installed a hidden shell script or apple script program and is capturing my screen and maybe sending it over the net. I don't know where to look or how to turn this off.

I have checked activity monitor and did not notice any programs running like "screencapture" or anything else like that. I have also turned hidden files visable on, but i can't find any screen capture directory or files: .jpg, .pdf, .png files I should be seeing lots of them for every 30 seconds per capture.

I have also installed little snitch, nothing strange seems to be going out by way of connections. Only dropbox, i have deleted that but the noise still keeps going. I will have to reinstall again..