What are the sounds of abnormal engine noises?

[SawyerLee]

Abnormal engine noises can be categorized into the following types: 1. The first is a high-pitched squealing sound from the belt: This is usually caused by belt slippage. 2. The second is a sharp metallic friction sound: This is generally due to damage to the bearings of the generator, water pump, or power steering pump. 3. The third is a tapping sound in the engine compartment: Due to gravity, all the lubricating oil in the engine flows back to the oil pan after the vehicle has been parked for a period of time. During a cold start, the oil pump needs to "transport" the oil from the oil pan back through the oil passages to various moving parts and friction pairs, establishing and maintaining a certain oil pressure. During the process of oil "transportation" and oil pressure buildup, an oil film has not yet formed between the components, especially the hydraulic lifters in the cylinder head, which need to go through an oil-filling process. At this time, the valve clearance is relatively large, resulting in normal mechanical "tapping" sounds when the valves close and seat.