Lol, I noticed that a couple of years ago with my v1. It's this little pip, pip, pip, pip... If you hold it really close to your ear when it's on the clock, it goes pip, tick, pip, tick, pip, tick...
The unit makes the sound every new frame. I think some of the eletric discharge from the LCD goes to the buzzer. Try holding it up to your ear while switching to clock mode.