The Piano Man is changing his tune. Just five months after Billy Joel snapped up this waterfront retreat for $7 million, it’s back on the market. A local real estate broker says Joel abruptly stopped renovations. Built in 1955, the traditional-style home sits on 5.6 acres with a tennis court, a pool, and a pool house. The property includes 340 feet of bayfront with a deepwater dock, a rare commodity. Sources say it appealed to Joel because he has a boat-building business. After famously selling his East Hampton home to Jerry Seinfeld two years ago for around $30 million, fickle buyer Joel bought a home on neighboring Shelter Island as well as another house near chez Seinfeld.