As of today, 1/22/13, when the car runs over railroad tracks or bumpy spots in the road I hear a noise like rocks ratling around under the hood on the drivers side front. It might be coming from the left front wheel well. It's hard to tell for certain. When the car is driven over smooth road the noise disappears. I just had this car at the dealer 3 weeks ago and had them check it over and was told everything looked fine. What could this be?