my expe is making some funky sound , it started two days ago , i was reversing and heard some vibration like sound , then at a stop again i heard it not sure how to discribe but i woud say it is like underbody plastic vibrating , i tried putting it revers, applying the parking breka and getting out to listen ...i even opened the hood and nothing .so i got back in took brake off started parking it and sure enough there was the sound again ,,,,,does anyone have a clue?????