I often see something like that when I'm driving and stop behind a car that has LED tail and brake lights including an LED brake light above the rear window. I

I often see something like that when I'm driving and stop behind a car that has LED tail and brake lights including an LED brake light above the rear window. If I look at the car's rear trunk lid and hold my eyes still for a few seconds, the raised brake light starts moving up! (Or down, I don't remember which direction right now, but I think it's always the same direction.) And it's not like everything in my vision is moving with it, that one raised light is moving all by itself. And it keeps moving and moving in the same direction, but somehow stays in the same place. It's a strange experience, almost like a Shepard Tone of vision. https://www.google.com/search?q=shepard+tone https://www.google.com/search?q=shepard+tone