Every so often a Rolling Stones earbug will take over. It happened last March in Hanoi with “Monkey Man.” Now it’s “Backstreet Girl” — a gentle mood piece with a waltzy tempo. Well, not lyrically “gentle” — it’s actually an ode to heartlessness and diminishment in which a married guy tells a sometime girlfriend to keep her distance. But the musical accompaniment — vibraphone (Brian Jones), harpsichord (Jack Nitzsche) and accordion (Nick de Carolulls) — lulls and soothes. Especially the accordion. The arrangement argues with the content and vice versa, but that’s the odd charm of it. Again, the mp3.