What is the cause of the popping sound from the exhaust pipe?

[WalterLee]

Popping sound from the exhaust pipe is caused by accumulated water inside the exhaust pipe. When gasoline is completely burned, it produces water and carbon dioxide. At high temperatures, water exists as water vapor, which is colorless and transparent. However, when the temperature drops below 100 degrees Celsius, the water vapor condenses into water and accumulates. The water droplets discharged from the exhaust pipe are the result of water vapor generated by gasoline combustion condensing in the exhaust pipe and muffler. The exhaust pipe is part of the engine's exhaust system, which mainly includes the exhaust manifold, exhaust pipe, and muffler. Typically, the three-way catalytic converter, which controls engine pollutant emissions, is also installed in the exhaust system. The exhaust pipe generally consists of a front exhaust pipe and a rear exhaust pipe.