There are many potential causes for engine knocking noises, and they vary slightly from one vehicle to another. However, there are a few causes of knocking noises that are much more common than others. Some of the usual causes for a knocking sound from a vehicle's engine are low-quality fuel, incorrect spark plugs and deposits forming on the engine's cylinder walls, according to HowStuffWorks.
Engine knocking can be a very worrisome problem, but it is also relatively common. Because of the diverse causes of knocking sounds, it is difficult to ascertain the severity of the car's problem based on the engine knocking alone, notes HowStuffWorks.
Low-quality fuels can cause engine knocking. This is because inferior gasoline and octane results in adverse changes to the car's fuel chamber, including fluctuating temperatures and pressures. This causes fuel to ignite and burn prematurely, which leads to repeated engine knocking. Another problem that leads to engine knocking is the buildup of leftover fuel in the gas chamber. This is another symptom that stems from low-quality fuels. If a vehicle has the wrong spark plugs, they can also fail to adequately regulate the conditions inside of the fuel chamber, which leads to the same issues.