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.
Abnormal engine noise is due to excessive clearance between two internal metal parts that should have little to no clearance. This clearance can be due to many things from a broken valve spring to a crankshaft bearing that has failed. The first step is to identify where the engine noise is being generated. With the engine running isolate where the noise is coming from in either the the upper half, lower half, front half or rear half. Listen from above and below the engine as this will help determine where to start looking for the cause of the noise.