It sounds to me like you were merely holding the camera in such a way that you were smothering the microphone. You can see that the audio becomes muffled (or restored) as you change your grip on the camera. And when muffled, the clicking sound is the autofocus and/or aperture mechanism -- made very apparent by blocking external sound. So, it's avoidable. You just need to be more careful in how you hold the camera. (Don't blame the innocent ! ;-)