when my battery was low or had corroded terminals my lights did this.

 

mine only do it on the highest setting. i have a new battery and perfect terminals so my temp fix has been to adjust my lights higher than needed and run them a few notches down

 

I have mine between the 1 and 2 mark or else it will moving up and down.

 

I stopped mine by unplugging the adjustment motors on the actual headlights. There is a thread on here somewhere that shows you which ones to unplug, but it's fairly obvious once you get behind the headlights and look.