It might not be easy going back to sleep after your house startles you awake, but it’s likely nothing to worry about.
Are roof trusses the culprit?
For 50 years most house roofs have been framed using triangular assemblies of wood called trusses. The top two sides of each truss sit directly below the roof surface, where the wood is subject to wide swings in temperature and humidity from winter to summer and vice versa. This leads to changes in length that don’t happen nearly as much on the bottom side of the truss. The occasional thump in the night is the sudden release of pressure within the truss caused by these changing differences in length. It may sound alarming, but it’s nothing to worry about.