Sounds to me as though he's reacting to the belly rubs. I have very few here that actually adore belly rubs! Maybe you can make him a toy that he can beat on when he gets fired up! I use my husbands tube socks, stuff them with pillow stuffing, pour in a whole bunch of catnip, and tie the top with some strong string. They don't last very long though....the cats go nuts with them!