I just had all 4 tires replaced three weeks ago at the local dealer. Since then I have had a sound like rocks or pebbles hitting the rear wheel well when going over a depression but highly intermittent. Might only happen once or twice in a 40 mile trip. I just had the car in to the dealer today complaining that there must be something loose inside the driver side rear tire. Drove them crazy looking for a ghost. Maybe it is just the rear hatch as mentioned above? I will be trying the bumper adjust tomorrow. Surprised they did not mention the hatch if so many owners are having that problem.