ARLINGTON, Va. — It sounded like popcorn warming in a microwave: sporadic bursts that quickened, gradually, to an arrhythmic clatter. “There it is,” Mary McKee said, staring out the front door of her home in Arlington, Virginia, on a recent afternoon. McKee, 43, a conference planner, moved to the neighborhood in 2005 and for the next decade and a half enjoyed a mostly tranquil existence. Then came the pickleball players. Sign up for The Morning newsletter from the New York Times She gestured acr