This happened to me when I kept my snakes in my bedroom. I'd play my music pretty darn loud, and they would always come out and take a peek at what was happening (my YB used to do a full-out periscope when I listened to Tool, like she was trying to dance to it LOL)
What it is is they can feel the vibrations through the cage floor and their belly, and so they're coming out to check out what's going on. That's my theory, at least. Because they do sense vibrations, and it may seem like a wicked storm or something else that they recognize at an instinctual level.