Jake Gyllenhaal has been turning heads — or “spinning” them — by popping up on the “instructor’s bike” at SoulCycle in Union Square. The “Source Code” star cycled on a stage next to an instructor Monday in full view of an afternoon spin class. He even mouthed the words to a Jay-Z song playing on the soundtrack while wearing “a black tank top, shorts and full beard dripping in sweat,” a spy said, adding Jake even lip-synced, “I got 99 problems but a bitch ain’t one.”