We just picked up our 2021 Leaf Thursday evening. We were just out for a drive, had the e-Pedal engaged. Put down the passenger-side rear window and was hearing a thutter, about like a Huey UH-1 that we didn't hear with the window up. It started at about 20 mph and got louder and faster as we went to 45 mph. Is this just breaking it in? Or is it an item of concern?