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.
Without a properly working knock sensor your car's engine cannot process fuel without knocking, pinging, and rattling its way down the street. Turn off your car when the knock sensor is dead and you are likely to witness your car shaking, gasping, and rattling for several seconds after you turn off the ignition.