Old doorknobs make a very particular sound.
It’s a hollow rattle, metal on metal in a tight gap. That sound of a space being entered—it’ll carry to all the rooms in a quiet house.
A doorknob rattling is perfect punctuation for a scene: something’s right on the boundary, on the edge of crossing over a threshold, into the realm of the narrative.
It creates a delicious tension about what’s on the other side, rooted in the disturbing realization of just how thin the wood of a door really is.