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With un-altered females, a 'chirping' type of cat vocalization is a signal she's in heat (ovulating and ready for a mate.) They may also howl mournfully, if they are isolated from males.
Another possible reason for a cat's rapid clacking of it's teeth, is if it's excited by the prospect of a kill - I've heard this clicking sound when my cat has her eyes on a bird which has wandered close to the window.
My cat, Roarie, is an un-altered female, but she chirps when I call her name and she wants to be petted, or if I have food that she wants. Sort of like a sweet way of saying, "I see you, whatcha got there?" She has done this since she was really young, before being physically mature enough to go into heat. So, I think there may be more to cat chirping than the two things listed. It's not a teeth clattering, it's actual chirping.
dats da same with my female cat and its only 4 months old.
My fixed male cat does this too, as if to say "hey mom, sup." Very cute!