Subways singing "Somewhere"

Since 2000, some subway trains in New York City have been singing the first three notes of Leonard Bernstein and Stephen's Sondheim's "Somewhere" while leaving a station. Sort of:

The sound is a fluke. Newer trains run on alternating current, but the third rail delivers direct current; inverters chop it into frequencies that can be used by the alternating current motors, said Jeff Hakner, a professor of electrical engineering at Cooper Union. The frequencies excite the steel, he said, which — in the case of the R142 subway cars — responds by singing "Somewhere." Inverters on other trains run at different frequencies and thus are not gifted with such a recognizable song.

Stop, look, and listen:

Under Broadway, the Subway Hums Bernstein (New York Times)

(Thanks to Stefan Hagemann for making sure that I saw this article.)