Why does the car feel the engine sound louder after cleaning the carbon deposit?

After cleaning up the carbon deposit, the combustion is more complete, the power rises and the sound naturally increases.

It is reasonable to say that there will be no engine noise when changing oil, unless the hydraulic tappet oil can't get in and the tappet makes abnormal noise. However, it seems that Corolla is not a hydraulic tappet but an adjustable VVT-I, and the noise caused by the engine cleaning agent package, so the determination of responsibility is very different from that before leaving the factory. Some original air filters may not be like this. Unless it is installed incorrectly, it is the noise generated by other vibrations, and the cleaning oil circuit will not produce abnormal noise. Cleaning the three-way catalytic converter may not be noisy, but it depends on how to clean it. If the engine itself has too much carbon, it will be blocked in the three-way catalytic converter after cleaning, and the exhaust sound will also increase, which may be mistaken for the noise of the engine. If it is such a noise, it is also the responsibility of the 4S shop, but there is no standard to judge the noise. No one can tell you exactly what your original sound is like, so it's not an abnormal engine sound, so you may have no idea about it, or your own psychological function may feel better.