"some kind of weird Doppler effect"

The Doppler effect is named after the Austrian physicist Christian Doppler (1803-1853) who explored the way a sound wave changes frequency from the point of view of an observer if the source of the sound moves. Thus a police car siren sounds higher in pitch when the car is moving towards an observer and lower in pitch when it is moving away. This is because sound waves are compressed when the car is approaching the observer and elongated when the car is retreating.