Just to think out loud...
A bite can be a self defense thing or a "checking it out" thing.
If it's self defense (stopping an action he doesn't like or is afraid of), usually they crab first. But I suppose there could be those that don't want to waist the time talking (I feel like that myself alot lately :-/
So my question would be... when is the biting happening? The answer may be to to first figure out the CAUSE of the biting.
But if it's not a defensive thing, it may be a phase, or him looking for more treat from you - so many reasons.
Without being there to watch his behavior, I'd almost have to ask you to keep a record of his behaviors and yours leading up to the bites for a few days so we could read it and make some educated guesses.