The bell after the line closed

An original narrative about an invented visit to a disused signal box.

I unlocked the signal box shortly after noon. The railway below had been closed for years, but the narrow room still appeared to be waiting for work to begin. A row of black levers stood beside the windows. On the desk, a timetable remained pinned beneath a wooden ruler, and the hands of the wall clock had stopped at twenty past four.

I had come to record the faded labels before the building was repaired. As I copied the first one, the wind pressed against the walls and released them with a long wooden sigh. Dust stirred along the desk. None of this surprised me.

The bell did.

It gave one clear note from the shelf behind my shoulder. A loose wire descended from it and crossed the floor in a series of dark loops. I watched the loops, expecting one of them to tighten, but they remained still.

I returned to the labels. This time, I kept the bell at the edge of my sight. Several minutes passed before it rang again. The second note was no louder, yet it seemed nearer because I had been waiting for it.

When I bent to collect my bag, I found that one loop of wire had caught around its buckle. That explained it, I told myself. Each time I had moved the bag, I must have pulled the wire. I freed the buckle and laid the wire flat against the floor.

At the door, I looked back. The wire had not moved. The bell's small metal clapper was swinging gently from side to side.

How does the writer create unease in the signal box, and how far does the final paragraph explain what has happened?