I have the same problem. but still havent found out what is wrong. I took mine to my local ford dealership and even went with one of the pr_cks to show them what I meant and they said it was normal ( normal as in they could hit me for more money when things really screw up). So I just said poop on it and forgot about it till last week when I was passing someone on the way to visit my girlfriend and it happened again. I wouldnt mind knowing why it happens