My parakeet keeps biting me!?

Im not talking about a nibble but a full and fast neck extending hard bite. Whats wierd is that it pretty much only happens at night around 11:00pm - 6:00am. In the day, he is fine & he loves to play and there is no problem getting him to perch on my finger day or night. This starting happening about 4 days ago. As I approch in his cage he opens his beak to the fullest and looks like he gets bigger, and then If I get closer he snatches at me. He is so nice and was even nicer before he got like this. I have had him for about 2 months. But he is probably about 9-10months old. Some one told me that this is when they hit "puberty" and they become more dominent. PLEASE HELP!