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.
What causes a loud knocking noise in the engine? Usually, knocking indicates bad bearings on the crankshaft. You are going to have to budget for a rebuild on the bottom end of the engine.