Why did you stay in a hotel at night? The sound of cylinder collision is

Affected by building pressure and the existence of mold.

When an object is heated, its volume will increase; if it is cold, it will shrink. This will also happen on buildings. The concrete in the building will expand when heated during the day, but will shrink when the temperature drops suddenly in the middle of the night. The so-called sound of cylinder collision is the sound made by the extrusion of concrete and steel bars in buildings.

Another factor is the existence of mold.

In some cities in the south, mold is often produced in houses in summer. These molds rise to the interior of the building along the cracks in the building and come into contact with building materials such as steel bars. Over time, steel bars will produce a hollow pipe under the erosion of mold. When it is hot, the steel bar will fill the whole pipeline, but when it is cold, it will shrink, resulting in a crackling sound.

And these sounds spread through hollow pipes are also heard as the sound of cylinder collision.