I think the noise you heard was probably the sound they make when they're upset (squeaky dog toy) and want attention (or food, or something...)
Mine will do that when they're dreaming, or if I'm late to wake up and give them their treats at the usual time.
The chirp sound sounds just like a chirp. When mine chrip I call them my little peepers! It's so cute, because you know they want you to love them up!
Usually they chirp a few times and then rapidly in succession, the noise that begs for attention. It's soft and calm, not panicked and shrill like the 'dog toy' noise.
At least, this is my experience!