What is the reason for the noise at the intake of diesel engine?

There are several main reasons for the noise at the intake of diesel engine: ① the pressure pulsation of air in the intake pipe produces low-frequency noise; (2) When the air flows through the intake valve at high speed, it forms vortex and produces high-frequency noise; ③ Forced vibration of the gas in the cylinder under a certain pressure, the sound of valve seating and the vibration of the intake pipe, etc. ④ Noise of scavenging pump of two-stroke internal combustion engine.