The inclusion of the sound is anachronistic, but it’s a distinctively New York Easter egg. When they get into a train and head off to the Cloisters for a date, you can hear that distinctive minor-seventh resolving to major-sixth screech. In the film, Tony and María decide to rendezvous at a subway station after meeting in secret at her balcony after the dance. It rises a minor seventh and then resolves down a half-step to a major sixth, a sequence of notes that just so happens to trace the opening phrase “There’s a place” from the song “Somewhere” in West Side Story (it’s also the reference that some music theory teachers, or at least my music theory teacher, use to teach you what a minor seventh sounds like in the first place).
If you’ve taken the subway a lot in New York City, you might be familiar with a peculiar, whirring three-note refrain that plays just as some of the trains pull out of the station. But in his film adaptation of West Side Story, one of those motifs pops up in an unlikely source: the New York City subway. In a musical, it’s standard practice to scatter the motifs from your songs into your score, using them to thread together whatever emotional echoes you want to reverberate throughout the story. Transit nerds, Steven Spielberg has a gift for you.