Your guy was a stray previously, yes? That could have something to do with it. Animals who've spent time on their own "in the wild" sometimes freak out about the whole regular meals thing...it becomes an obsession.

Or he could just be like my Chow Chow, who in her old age has decided that no amount of food is ever enough...to the point where she dove into a bag of Kibble recently and got through half the damn thing before I figured out what that weird noise was.