What causes engine knocking (and how can you prevent it)

Engine knocking can be an annoying issue to deal with, and it can even cause damage to your car. Here's why it might happen, and how you can prevent it.
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Ask Honest John - Why is my engine making a knocking sound when cold?

I have a SEAT Leon 2015. When cold there is a knocking noise coming from the engine. It sounds like it is in the area in ...