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.
A Diesel-Like Clattering in Your Gas-Powered Car. Worst-Case Scenario: Detonation, also known as pinging or knock. Why: Things like bad gasoline or incorrect ignition timing cause the fuel to go boom too early. If left unchecked, you risk serious engine damage. What To Do: Switch to higher octane gas, which resists detonation, and check the timing.