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    Why is there a knocking noise under the bonnet before starting the engine of my 2005 Holden Astra?

    Holden Holden Advice Holden Astra Holden Astra Advice Holden Astra 2005

    I hear a knocking noise under the bonnet on the driver’s side before starting the engine in my 2005 Holden Astra, what could be the problem here?

    Answered by CarsGuide
    9 September 2021
    David Morley

    You’d expect any noise from under a car’s bonnet to be caused by the engine, but if this noise occurs before you’ve started the engine, you’re on to a real mystery. Perhaps the noise can be heard as you crank the engine but before it actually fires? If that’s the case, the clunk or knock could be coming from the starter motor. Or perhaps the action of the starter motor is causing the engine to rock back and forth on worn engine mounts and allowing the engine to hit on the cross-member or some other component under the bonnet. Perhaps it’s a loose exhaust system that’s banging on something as you crank the engine. Once the engine fires and is running, the frequency of its vibrations changes and the clunk goes away.

    But I’m afraid that without more information, this one remains a mystery to us.

    Disclaimer: You acknowledge and agree that all answers are provided as a general guide only and should not be relied upon as bespoke advice. Carsguide is not liable for the accuracy of any information provided in the answers.
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