"Knocking sounds" refer to the noise produced when a solid object strikes another surface. This can occur in various contexts, such as when someone taps on a door or when objects collide. The sound's characteristics, like volume and pitch, depend on the materials involved and the force of the impact. In some cases, knocking sounds can indicate issues, such as in vehicles where they may signal engine problems. In homes, knocking noises in plumbing, often called water hammer, can occur when water flow is suddenly stopped. Understanding these sounds can help identify their sources and potential concerns.