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.
Worn out tie rod ends can cause the front wheels to shake or wobble and emit a hard knocking sound when brakes are applied, especially while driving at high speeds. This situation is extremely dangerous and the damaged components must immediately be replaced by a qualified mechanic, reports Driverside.com.