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.
3 Causes of Engine Knock. Engine knock is among the most disturbing problems a vehicle can have, but not many people know what it is, or how it is caused. Basically, engine knock (also known as pinging, detonation and spark knock) occurs when the air/fuel mixture inside a cylinder is incorrect, which makes the fuel burn unevenly.