Is he any better in different environments? Like..out of his cage and such? If he bites in the cage, like mine does, he may not like you around "his" stuff. They also recommend you don't put a mirror in his cage.

If not I'd say it's out of fear. Then you would need to take the steps on hand taming.

See: http://www.bellaonline.com/articles/art37897.asp