I had two remaining eggs in my brinsea where I could here them peeping without a pip.
They couldn't get through the hard shells. I pipped for them. The lived. (both were roos so I won't be passing on the tough shell gene in my flock as they've been rehomed)
I've only noticed peeping 12-24 hours before hatch on mine. The peeping comes from when the chick has internally pipped into the air cell. This only occurs right before hatching
Thanks TGarcia,Mahroni, & abanjaf! My hen is sitting tight on those 4 eggs, I'll sneak out there one more time today Hatching's due on Thursday. I swear I'm almost more excited than a kid on Christmas eve!