Definition of discourse marker noun from the Oxford Advanced Learner's Dictionary
When an engine starts knocking, one of the first things a mechanic will check is the oil pressure. A warning light may come on in the car, and adding sufficient oil will solve the problem. Sometimes, a knocking noise is caused by loose torque converter bolts or a loose flywheel.
Up to a point, more power can be produced. in an engine by increasing spark advance. But. too much advance causes engine knock. Once knock starts, performance decreases. and there is a risk of serious engine damage. Knock gets its name because it causes. vibrations and banging in the cylinder.