After the Audi a4 put out the fire, there was an electric current sound in the car.

You can't hear the current in the car, but what you can hear is the sound of the motor turning. After the car is turned off, in order to protect the machine parts, several parts are delayed to stop, such as the electronic fan of the water tank and the heat exchange fan of the air conditioner. After stopping, they will delay their work for a while and let the temperature slowly return to normal temperature. So you may hear the sound of the motor turning.