My Cresties chirp, thats the only way I can explain it. Its only when one or more are housed together.
Now my Tokay on the other hand is LOUD. Every night, several times a night I hear Tok-aaayy over, and over, and over again.
I have figured out how to make him do it too. I go upstairs, turn on the light in the bedroom for a few minutes, than leave and turn it off. Never fails, within 5 minutes he is at it again. I think its the mating call.