What Causes the Sudden Abnormal Noise at the Moment of Successful Ignition?
3 Answers
Here are the main reasons for the sudden abnormal noise at the moment of successful ignition in a car: Incorrect gear shifting and clutch operation: The gear is engaged, and the clutch is not fully depressed. Starter motor slipping: At the moment of ignition, the car's starter motor slips, causing the noise. Excessive cranking time: Prolonged cranking leads to the flywheel hitting the starter gear at the moment of successful ignition. Belt slipping: During ignition, belt slipping may also cause abnormal noise, but this usually disappears once the engine belt reaches operating speed. Note: It is recommended to have the vehicle inspected at a repair shop as soon as possible for the above reasons, otherwise it may affect the vehicle's lifespan.
Hearing abnormal noises at the moment of ignition can indeed be quite nerve-wracking. I've encountered a similar situation before, and it turned out to be an issue with the starter motor. The drive gear inside the motor retracts immediately after ignition, and if the return spring fails or the gear gets stuck, it can be spun by the flywheel when the engine starts, producing that metallic scraping or clattering sound. Another common cause is wear on the flywheel ring gear, especially in older vehicles with high mileage—worn gear teeth can lead to slipping. Belts shouldn't be overlooked either; during engine startup, the sudden surge in RPM can cause aged or loose belts to tighten abruptly, resulting in a squealing noise. There are also less common reasons, such as a leaking exhaust manifold gasket, where the ignition shock can produce a popping sound at the leak point. For safety, it's best to get it checked as soon as possible. Ignoring these minor issues for too long can really damage the starter motor or flywheel beyond repair.
My car used to make a clicking sound when starting, and the mechanic said it was a starter motor bendix failure. The bendix should retract when starting but got stuck, and the flywheel forcibly dragged it, causing gear grinding. Flywheel ring gear wear can also cause grinding noises, especially more noticeable in winter when metal contracts due to low temperatures. Additionally, the squealing sound of an aged belt under sudden load during startup can easily be mistaken for abnormal noise. If the exhaust pipe gasket is leaking, there will be a whistling-like puffing sound, usually more pronounced during a cold start. Also, in cars with loose timing chains, chain vibration hitting the guide rails during startup can produce abnormal noises. The simplest method is to have someone assist with starting the engine while you open the hood to listen for the source of the sound, which can roughly determine whether it's an issue with the motor area or the exhaust pipe.
