Q: Knocking sound.

A knocking sound within the engine is likely caused by low oil. I would first start by checking the oil level to ensure it is full. If the oil is low, you can top it off and see if anything changes. If nothing changes, permanent engine damage may have occurred. Sometimes parts of the engines valve train can be replaced to fix this issue but much of the time a new engine is necessary to get rid of the noise. When the lubricant between moving parts is gone metal will start to shave away from both metal surfaces. Once enough metal is removed, a gap will exist causing the knocking sound. I would recommend having your engine inspected by a professional to ensure the problem gets diagnosed correctly.