Why does the car make noise after driving?

[RyleeMarie]

Here are the reasons why a car makes noise after driving: 1. Three-way catalytic converter cooling sound: The normal operating temperature of the three-way catalytic converter is 400-800°C. After turning off the engine, its operation gradually stops, and the temperature decreases, causing the internal metal components to expand and contract due to heat, resulting in abnormal noise. 2. Exhaust pipe cooling sound: During cold idle, the exhaust pipe can reach temperatures above 200°C. When the car is under high load or there is a mixture of gases burning in the exhaust pipe, the temperature can be even higher. Therefore, the exhaust pipe also expands and contracts due to heat, producing abnormal noise. In many cases, this sound comes from the front end of the exhaust pipe and the flexible connection. 3. Turbocharger cooling sound: Under normal conditions, the exhaust gas temperature can reach 600-700°C, accelerating the rapid rotation and friction of the turbocharger, which generates heat. After turning off the engine, the heat expansion and contraction become very noticeable, leading to abnormal noise. 4. Engine cooling unevenness causing noise: After driving for a while, the engine temperature becomes very high. After turning off the engine, the temperature of various components decreases, and the heat expansion and contraction cannot occur uniformly. This inevitably leads to gaps between the internal metal components of the engine, causing friction and abnormal noise due to cooling contraction.