physical mystery

Here comes a physics question. I constructed the kinetic toy shown below from "GeoMag" magnets and steel balls, it's suspended from the ceiling and has two joints that move freely, i.e. the places where two steel balls touch directly. So there are three parts that are independent of each other. If I spin the bottom part quite fast, the middle part will rotate too (but not as fast, I think), will then stop, rotate for a while again, etc.



Any clues ?

I'm thinking the magnetic field of the dumbbell in the middle should be symmetrical with respect to the rotation axis, so I can't think of a magnetic reason for this "behaviour". Maybe it's just random small differences in the friction depending on how the balls touch. But in any case it's fascinating to watch and procrastinate over ...