Most likely a belt.
whistle
A whistle is a High Pitch because its really loud and not really low.
The train's whistle can change in pitch over time.
What cause a whistle song on my gmc jimmy
The sound a whistle makes is often described as "whoo" or "wee" depending on the pitch and intensity of the sound.
it depends on the length
A whistle makes a high sound because of the short length of the whistle's tube, which amplifies high-frequency sounds. When air is blown into the whistle and vibrates at a high frequency, it produces a high-pitched sound.
The raising and lowering of the whistle's pitch due to the alteration in the relative speed of the whistle as it goes by you, described by two terms that can be discovered by reading your homework assignment.
but crack
the pitch doesnt actually change but it might sound quieter to you because the sound it being blown away
This is known as the Doppler effect. As the train approaches you, the wavelength of the sound waves it emits are compressed, and therefore the whistle sounds higher. When the train is moving away, the wavelengths are extended, causing the whistle to sound lower. If the train were not moving at all, the pitch you would hear from the whistle would be somewhere between the high and low pitches you hear when the train is moving.
Since you are also on the moving train, the pitch should remain constant.