Invisible Ghost Causing Squeaky Stairs

An old man is sleeping and suddenly hears his stairs creaking as if a ghost or an invisible man is walking up and down the stairs.

It is not ghosts or invisible people ,it is expansion and compression causing the wood boards to creak depending on the temperature and/or weather changes. Not because some "ghost" is walking up and down the stairs.

Should one worry about creaky stairs or even floors ? No, if one does not hear the creaks it could either mean the floor boards were nailed too tight or someone fixed the creaks by putting small mental screws underneath the floors plywood.

These mental screws will also expand or compress along with the floor boards making them still safe; After all, having the floor board too tight will cause problems, like splitting into two or more pieces causing holes and weaken floors.