The 4 train as it leaves 59th Street station
Hear it for yourself from this youtube video
Recently, the New York Times ran a story about some NYC subway trains making electronic whine that sounds just like the first three notes of Leonard Bernstein's “Somewhere,” a ballad from the musical "WEST SIDE STORY." I hadn't noticed this since I rarely take the 2, 4 and 5 lines. The other day, I took the 4 train just to hear the sound when the cars start moving. And finally I heard! "There's a place...." But I still don't know what the big deal is.
Careful listeners have been hearing the sound beneath Broadway since 2000 when new cars began using an innovative propulsion system, said Gene Sansone, the chief mechanical officer for the subway.
The newer trains run on alternating current that is chopped into frequencies that excite the steel and produce the sounds, in this case the beginning of "Somewhere," said Jeff Hakner, a professor of electrical engineering at Cooper Union. Other trains, running at different frequencies, fail to produce such a recognizable sound.
The music from "West Side Story" was composed by Leonard Bernstein. The musical opened on Broadway in 1957 and was made into a movie in 1961, both earning multiple awards. Currently, a new revival is in previews at the Palace Theatre.