I have the exact same problem with my two. Sammy is 7mos and Sadie is 5mos. They fight like crazy. I can't tell who starts the fights, but they sometimes growl so loud, we can't hear the tv. When they do this, I try to seperate them but they go right back at it. I have just started using a squirt bottle of water and squirt them, and that seems to stop it for a while. Sammy likes to tease Sadie with his bone or toys, and when she goes after whatever he has, it makes him mad and then they start all over. It gets on my nerves really bad
He even tries to pull her off the furniture by her hair or ears, but then she does the same to him. I am reading all the posts to see if I can pick up something helpful too.