ok erm. heres a few possiblilites. Obviosuly because he is a pup its harder to understand what he is trying to say, but even as pups dogs always let the boss know hes the boss, but as he is a pup i can't see it as being aggression. while i was studing animal behaviour at college we were told that it it usely because the pup is nervous, scared or just unaware of how to communicate, hensh the barking. Have you raised him yourself or do you know his past?