Oh,you have a younger child? That could be where the problem lies. How well did you prepare the kid for the arrival of the new baby? Remember he was used to getting all the attention before the new baby. Are you and your wife now treating him as a 'grown'up and giving all the attention to the little child? He may be feeling left out or displaced and hence the anger in him for not getting enough attention and doesnt know how to express it. Infact,the people who come to see the baby make it worse but gushing how cute the baby is,how beautiful/handsome,you know all that baby talk... and for him??? nothing. however,you can help him to deal with the anger by showing him more love,creating time just for him especially when baby sleeps,getting him to help with the baby - like wiping him etc but yes,he will need the same attention he used to get before the baby arrived.
check out this - you can google for more.... to get differnt perspectives of where the kid may be coming from.
http://www.sover.net/~th...lry%20&%20baby.html
http://aces.nmsu.edu/pubs/_f/f-213.pdf
Some deals are like glass. Sometimes it's better to leave them broken than try to hurt yourself putting it back together.