Calling All Scientists

Weird phenomenon this morning. I'm driving down the highway and notice that my exterior antenna is shaking back and forth in a violent manner. I'd never seen that before no matter how windy it was. This goes on for a couple of minutes and then it stopped for a while. Then the shaking returned. The cycle repeated itself throughout the journey. So I started to notice other cars that passed me. Some had the possessed and shaking antennas. Some did not. Ice was building up on my antenna due to the fog, but that's the only unusual thing. Ideas? I'm telling ya, it was weird.