Genuinely, no one is sure about why cockatiel parrots grind their beak.
Although, it is clear that this cockatiel behavior is not similar to the teeth grinding in humans, which symbolize anxiety.
Beak grinding shows the behavior of relief and a comfortable state of mind. Also, Utmost cockatiel parrots grind their beaks simply before sleeping or when they are in the strong mood of resting. White-faced cockatiel and Lutino Cockatiel Types and Lifespan are same.