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 could be the knocking noise coming from the engine area? There is a knocking sound that started coming from my car a couple days ago. It's not a ticking or a clanking knock. It's more of the sound when you take your fisted hand and starting from an inch above a wooden desktop tap at about 1 knock per second.