what is that noise before and after commercials?

Donald Bellisario wanted to do something different and original before and after commercials, and so he went into a back room with a microphone and made that sound to go with the black and white shots.

I have heard that it is a noise that Donald Bellisario made up and I beleive it is him making the noise.

It's the sound of a camera taking a picture. I believe it was actually the flashbulb that made the sound on old black and white cameras.