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.
This is a car engine that has a ping. Also called spark knock, preignition or detonation. If left uncorrected it can ruin the motor. Caused by either a lean fuel condition, carbon deposits in the combustion chamber, over advanced ignition timing, wrong spark plugs, or overheating.