fred was like this! even chewing on an alexander repeatedly
only for attention, you walk over and he would walk to the door and wait to come out.
he was also cage teritorial
if bert is the same try using a tube, cup or ball to walk into, then get them out, i find them far less likely to bite outside the cage, once they are fine with you handling them outside (normaly on the bed for me) then you can try getting them to walk on your hand or picking them up, fred still today tutters if i put my hand in the cage, but he is the only one of mine i know will never bite me again, i can turn him over and blow a rasberry on his belly and he wouldnt bite xD hes a silly boy