For 1990-2009 cars

Problem | Cause
--- | ---
High pitched whine during cranking (before engine fires) but engine cranks and fires okay. | Distance too great between starter pinion and flywheel.
High pitched whine after engine fires as key is being released. Engine cranks and fires okay. This intermittent complaint is often diagnosed as starter hang-in or solenoid weak. | Distance too small between starter pinion and flywheel. Flywheel runout contributes to the intermittent nature.
A loud whoop after the engine fires but while the starter is still held engaged. Sounds like a siren if the engine is revved while the starter is engaged. | Most probable cause is defective starter motor clutch. A new clutch will often correct this problem.
A rumble, growl or (in severe cases) a knock as the starter is coasting down to a stop after starting the engine. | Most probable cause is a bent or unbalanced starter motor armature. A new armature will often correct this problem.