Luna rubs her teeth when she's annoyed and/or frustrated. She'll do it at me if I keep stopping her going somewhere (like off the edge of the sofa!) or when she's busy chewing boxes in her playpen and I'm trying to get her to come out
Never heard her make these sorts of noises though! She squeaks too - woke me up at 4am last night doing it
Haven't worked out why she does that though.