This may sound a little strange but the top of the rear bumper seems to get more dirt on it faster than rest of the car. the car can look fairly clean but the rear tailgate and the top of the bumper get very dirty. It detracts from the rest of the vehicle plus can get on your clothes when emptying the rear trunk area of groceries. Any ideas why this is occurring and what can be done to correct it. Is this due to no mud flaps on the rear wheels? Is there something with the aerodynamics? Thanks.