Loud knocks in your engine are not to be ignored rather you have to pay attention and give immediate inspection before it leads you to a severe situation. I would like to share with you and experience to explain what these mean to a car owner.
My friend and her wife traveled around 60 kilometers distance using their 1996 model Toyota L, Tamaraw series, jitney type AUV. Approximately 30 kilometers far from their point of destination and they are bound to they have noticed knocking of engine parts.
Hearing that tolerable but disturbing sound, the loud knocks, they continued and were able to reach a ten-kilometer distance. As they climbed up the road the car stalled. They rested for a while to cool the engine that is above 180 degrees F temperature. Maybe the temperature gauge was not functioning correctly because 180 degrees is still tolerable.
The engine was started and upon trying to advance had a loud knock and right there the engine is dead. They left their car in the rural site taking a bus down to the town. The following day their car was towed to a mechanic to their shop for an engine overhaul.
Possible causes could be traced from several reasons like overused oil, lack of oil, defective valve seats, valves.
Never ignore symptoms rather address it immediately and you will save time and money. Check here.