It's supposed to be a "heartbeat"... It's beeping steadily now on my v3. "Heartbeats" are most common when your Tamagotchi is a baby/ toddler or sleeping
It's caused by a circuit (LCD circuit I think) lighting up pixels on the Tama. It seems to be in synch with the animations. The "Z" you see when your Tama is sleeping is a good example
Some people also say that beeping is the clock ticker. You know, that thingy that keeps the time. The beeps are in synch with the little hearts that tell the seconds. But one thing puzzles me: The beeping acually GETS SLOWER when I'm at the clock screen. It goes like this: Beep. *Skip*. Beep. *Skip* ect. But when Im at the main screen, it beeps steadily. Hope this helped.