Thelmalu, I think what you have going on is just really play. My two guys go at it usually every couple of days. It doesn't last long but they tumble and roll all around and the fur flies! Andy, who is quite a bit smaller than Trevor, is ALWAYS the one who instigates these little sessions. It is also completely out of the blue, just like you describe. I think it's sort of an athletic event for him! The only problem is, when Trevor has had enough he usually lets Andy know and a short little chase follows with Andy making a mad dash through the door flap to the basement. Then they are back to their mutual grooming and cuddling until Andy gets the urge again and it starts all over!