I've heard my keets peeping up to a couple days before they even pip. They do peep a lot during the hatching process too. And oh lordy, first one hatched is always a loudmouth! (but that stimulates the others to hatch).
I can always hear them peeping. first time I heard it, it was the neatest thing. Now its just a signal,,,,,,,,,, hey here we come.. and when they do that , I have noticed the others start pipping.... love it!!!!!!!!!!!