A small percentage of vehicles may require higher octane gasoline under certain operating conditions because of variations in engines of the same model due to manufacturing tolerances, or because of an unusual build-up of engine deposits. A small percentage of vehicles may knock because of variations in engines of the same model due to manufacturing tolerances, or because of an unusual build-up of engine deposits. Other factors such as extremely hot weather, changes in altitude or hard driving conditions (like towing a heavy load) may also cause knocking. Many modern vehicles are equipped with an electronic device that detects and eliminates light knocking before you hear it.