Those in cold climates running F1's will be experencing the Front End Thump noise when going in reverse and turning the wheels. Usually happens when the air temp is 20 degrees and less.....only way to fix it is to go with RSA's or a different tire. You feel it thump, as well as hear it. Chrysler is aware of it, and said it has no effect and does not hurt anything. So before you go running back and having the service dept rip apart the front end, know that it is probably the F1's.