What Causes the Clicking Sound in BMW's Chassis After Parking?

[MacVictoria]

There are many reasons for abnormal noises in the chassis of a BMW after parking. Below is a detailed analysis of the specific causes of these noises: 1. Cooling sound of the three-way catalytic converter: The normal operating temperature of the three-way catalytic converter is 400-800°C. After the engine is turned off, its operation gradually stops, and the temperature decreases. The metal components inside then undergo thermal expansion and contraction, resulting in abnormal noises. 2. Cooling sound of the exhaust pipe: Typically, the exhaust pipe reaches temperatures above 200°C during cold idling. Under high load or when the air-fuel mixture burns in the exhaust pipe, the temperature can be even higher. Consequently, the exhaust pipe also experiences thermal expansion and contraction, producing abnormal noises, often originating from the front end or flexible joint of the exhaust pipe. 3. Cooling sound of the turbocharger: Under normal conditions, exhaust gases can reach temperatures up to 700°C, accelerating the friction-induced heat in the rapidly spinning turbocharger. After shutdown, the thermal expansion and contraction are quite pronounced, leading to abnormal noises.