Yesterday evening, on the Harvard Square Red Line platform, there was a musician playing Andean instruments -- Spanish guitar and pan pipes. But something about the tune he was singing in Spanish, in a Latin style, didn't sound quite Latin. It sounded like an American tune, put through some serious changes -- but as long as he was singing, I couldn't figure out what. It took an instrumental break on the pipes, without the distraction of the Spanish lyrics, before I recognized the tune he was playing in an unaccustomed style: "I Did It My Way."