The Wichita Train Whistle Sings was created in 1968.

Yes. 'Train whistle' is a compound noun, which means that both 'train' and 'whistle' are nouns individually but here they work together. The word 'train' is applied to 'whistle' in the place of an adjective, that is, a word that describes the type of whistle.

But have you ever heard a wolf whistle?

Many compound nouns eventually run together, like handbook or cupboard, and maybe one day, wolfwhistle.

The train's whistle can change in pitch over time.

toot

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.