Nope. No place in particular, just wherever and whenever the mood strikes him.
It doesn't happen when they're eating or if Danny decides to hang out on the window sill (Elvis' favorite spot) or even when I'm giving Danny attention. It almost seems like Elvis is just like, hmmm, nothing better to do, let me go and pick a fight! LOL.

Do you think it's possible that maybe they're just playing rough with each other and I'm completely mistaken in thinking that they're fighting?