So I checked out that website that I told you about. The one that had alot of information on biting piggies on it. Aparently, piggy's biting could be for many reasons:
fear
traumatizing events, (dropping piggy)
teen age attitude
and the list goes on and on......
They also give some ideas on how to encourage piggy not to bite. So I will post this link, and hope it works. It's actually the GuineaLynx website. They give alot of information here. So hope this gives you a few ideas.
http://www.guinealynx.info/links.html#biting