What Causes the Crackling Sound After Turning Off the Car?

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After turning off the car, the crackling sound is caused by the three-way catalytic converter in the exhaust pipe cooling down. This is a normal phenomenon due to thermal expansion and contraction, and it does not affect the vehicle in any way. Below is some relevant information about the three-way catalytic converter: 1. The three-way catalytic converter is a purification device installed in the vehicle's exhaust system. During engine operation, it converts harmful substances in the exhaust gases into carbon dioxide, water, and nitrogen. 2. The three-way catalytic converter reaches very high temperatures during operation. When the vehicle is turned off, the metal inside the catalytic converter undergoes thermal contraction, producing the crackling sound. Therefore, there is no need to worry, as this sound does not affect the normal use of the vehicle.