What happened to Jetta's partner's whistle when he turned off the fire?

The engine exhaust valve, diesel engine exhaust gas recirculation valve (EGR) and gasoline engine throttle valve are not tightly sealed, which will cause the throttle car to whistle.

1. cooling sound of three-way catalyst: the normal working temperature of three-way catalyst is 400 to 800 degrees. After the flameout, its work will slowly stop and the temperature will drop. Internal metal parts will expand with heat and contract with cold, and then make abnormal noise.

2, the cooling sound of the exhaust pipe: When the cold car is idling, the exhaust pipe will also expand with heat and contract with cold.

3. Turbine cooling sound: Under normal circumstances, when the exhaust temperature reaches 6 to 700 degrees, the temperature generated by the friction caused by the accelerated and rapid rotation of the turbine will be obvious after the flameout, resulting in abnormal sound. The abnormal reason may be that the interface screw of three-way catalytic converter is loose, the solenoid valve of carbon canister is damaged, and the starter Ramada is not well attracted.