My 2013 is approaching my end of lease (and extended warranty of 50K) and plan to purchase, but have a concern about the fact that when in eco mode, the engine often chatters as if not getting enough gas. It feels like it needs to downshift. A push of the gas peddle gets it to downshift and the noise stops. However, now, even when not in eco mode, I get the same chatter or rattling sound but only between 1 and 2K rpms. Anyone know if this indicates a problem or one waiting in the wings? Not sure if I should buy or turn in at end of lease. Otherwise, a great car.