This is what I've been pondering too as a possible terrestrial explanation. Perhaps some fancy machinery can beam modified waveforms not only with microwaves,

This is what I've been pondering too as a possible terrestrial explanation. Perhaps some fancy machinery can beam modified waveforms not only with microwaves, but with frequencies high enough to reach infrared and/or visible light. And perhaps some kind of an elongated blob is the state of the art now. And later, as the technology matures, one might expect more detailed movie-prop like "UFOs" to appear. Hoping to see a TIE fighter or Jetsons' space car soon.