The pounding didn't go unnoticed, but it did take Jack a moment to decide on a response; on one hand, he was exhausted, and he knew Ennis could kick the door in if he wanted to. On the other hand, letting him get that riled up would probably just be more painful for them (mostly him), in the short term.
Finally, he gave in, heading to the door and undoing the locks. "Shit, cowboy, calm y'damn self. S'asleep."