My car's antenna moves up and down with certain changes of the radio station. For example, when I change from FM 99.7 to FM 105.3, the antenna raises farther (or lowers a little, I can't remember). And when I switch back to FM 99.7, it seems to go back to the original position. Is my car antenna broken? or is this a "feature". It bugs me cause everytime I change the station, I hear the antenna move and it gets irritating.