A few questions and suggestions. Are your wheels symetrical? That is, do they spiral in such a way that stuff might blow off them if they rotate one direction and not the other? Do your neighbors have a lot of dogs? Do you park next to a lawn sprinkler? Are you in the lower latitudes where the faster rotation of the earth might cause a prevailing magnetic effect?

My dealer rotates the tires every 7.5K miles. Read the manual, it is a factory recomendation. Should have been free the first time...