What causes the popping sound after turning off a BMW X5?

[DiDelaney]

There are several reasons why a BMW X5 may produce a popping sound after being turned off: Uneven engine cooling: After driving for a period of time, the engine temperature is very high. When turned off, the various components cool down at different rates due to thermal expansion and contraction, which can cause friction between metal parts inside the engine, resulting in unusual noises. Exhaust pipe cooling: During cold idle, the exhaust pipe temperature is generally around 200 degrees Celsius. When the vehicle is under high load or there is combustion of the air-fuel mixture in the exhaust pipe, the temperature can be even higher. As a result, the exhaust pipe also undergoes thermal expansion and contraction, producing unusual noises.