That sound waking you at 3 AM, not sure whether it came from your own throat or somewhere else in the darkness, grumbles in the night. They say the house settling is as though buildings have feelings and wood and nails have to stretch after supporting weight all day.
But occasionally the groan is natural. Pain that may be hidden during daytime hours reveals itself when defenses drop. Before you can stop it, the groan comes out. Lovers groaning in the night too use the same language, the same unconscious sounds drawn from deep in the chest for both delight and suffering. Bypassing the brain's exacting censorship, the body speaking its own tongue.
Though perhaps that's just how we explain noises we can't identify, the enigmatic creaks and moans of a world that Looks different after dark when everything known turns a little threatening, somewhat odd.