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.
The Causes of Internal Engine Knock, and How to Eliminate it. Abnormal combustion, more commonly known as knock or detonation, has been the limiting factor in internal combustion engine power generation since the discovery of the otto cycle itself.