What are the causes of abnormal noises when starting a car?

[LoganAnn]

There are several reasons for abnormal noises when starting a car: 1. If the car hasn't been used for a while, the engine oil will flow back to the oil pan, leaving the top of the engine (the valve chamber) without sufficient oil. Since the valves lack the sealing and lubrication provided by oil, a hissing sound may be heard from the bottom of the car when it's first started. This is a normal situation. 2. Apart from normal circumstances, if there is a loud noise when starting the car, it is most likely due to an issue with the engine belt. First, check the tightness of the engine belt. You can try pinching the drive belt with your fingers and twisting it. Note that this operation should be performed when the engine is cool, and the twist angle should generally be less than 90 degrees; otherwise, an adjustment is needed. Additionally, you can inspect the condition of the alternator belt, as the accessory belt might be the source of the abnormal noise.