Popcornbird has an ideal situation with her Tiels, that you and I don't have ScantyNebula. I cannot leave mine out and I truly believe that is why they scream at times. And days like yesterday...even when they have the chance to get out, they might still scream. Yesterday, it was Milly making so much noise and I have no idea what in the world was wrong with her!!! I don't think anything has to be wrong for them to occasionally burst out into loud yells, to tell you the truth. Temper tantrums, maybe?