Why engine knocks

Engine knock, or pinging, occurs when a separate pocket of air-fuel mixture ignites after the spark has ignited the air-fuel mixture within the combustion chamber. Engine knock can be prevented using higher octane fuels, retarding ignition timing, or by using a lower compression ratio, among other solutions. I suggest start with having the ignition system inspected.

Vehicle presence IS required for hands-on testing and audio conformation of "engine knock" ..