It is very important to make sure Pete is checked by your vet to eliminate any medical/treatment reasons why he might be showing aggressive behaviour towards your other male dog. In a multi dog household your dogs will have already worked out a loose pecking order and there are many reasons why this may have broken down. Sometimes dogs that have been ill lose status and then when they are feeling better want to regain a higher position again. It may be that the one of the dogs has begun to mature and is more of a threat. It may be a number of factors and really needs a professional qualified behaviourist to come along and carry out a full behavioural assessment of all your dogs to find out where they and you fit in. You might want to ask your vet for a referral or check out the APBC (Association for Pet Behaviral Counsellors) for one in your area or if you live in the US the equivalent. Meanwhile do not punish your dog for behaving like this or it might make the situation a lot worse. Make a note of when and why Pete is behaving like this, are there any patterns to his behaviour for instance is he only doing this in your presence or when you are not there. Is he trying to get something off Bear, is it when there is food around, or a toy? I hope this helps a little but when aggression is involved you need a lot more one to one advice by someone who can study the dogs behaviour.