What's the crackling sound under the car after turning off the engine?

[EmeryFitz]

Don't panic, this isn't a major issue. It's purely caused by the catalytic converter and is completely normal. Here's the explanation: 1. Definition of catalytic converter: It's a purification device in the automobile exhaust system that converts harmful substances in exhaust gases into carbon dioxide, water, and nitrogen. It can be called an environmental protection assistant. 2. Chemical reaction of catalytic converter: The catalytic converter operates at very high temperatures, nearly 1000°C. After turning off the engine, the metal inside undergoes thermal contraction, making the crackling sound perfectly normal.