One of my rats has Been attacking the other rat for no reason and they squeal a lot when they but no blood is drawn or anything. I noticed that the the rat that is being attacked never moves from his corner at the top of the cage. Today I had them out for free range and put the meaner rat back first bc he was trying to escape and kept the other one with me. When I put the other rat back the attacker rat immediately started fighting with him and chased him all the way back up to his corner. I was wondering if this is a normal behavior or I should be concerned.