I had to rescue three almost ready eggs today because their mother, having already hatched two chicks, let the remaining eggs go cold. One of them was already pipped and has since hatched and been put under mama once she was on the nest again, one of the other two has pipped and is - along with the expected chatter - making an extremely regular clicking sound. Is this normal? I can hear it without even holding the egg to my ear sometimes. They are in a diy incubator with approximate humidity and exact temp. I've hatched four eggs before without ever noticing this sound.