Yes, it's called 'beaking' and is the equivalent of the teething stage of children or puppies when they chew on everything. They often chomp down a bit too hard when they are babies because they are experimenting and don't yet know the strength in their beaks. Just take your finger/hand/whatever part of you he's biting and say something in a soft voice (I say 'gently, gently' and, when he does it gently, say, "Good boy, gently, good boy!' (or whatever command you are going to use) so they know what you mean by it and that the soft version of the chomping will elicit praise while the other will mean you will take your hand away.
I don't know what to tell you about your avian vet... I've never come across one that doesn't want to do tests or that says that one should not worry about symptoms.





