Judging by the trails of the rocks, the rocks have experienced friction at least from having to push the clay in front of them to their sides. There must have been some counterforce to propell the rocks forward. If this force was a mudstream pushing the rock from behind, I don't think the trail would have looked like this. The mudstream would have filled up the trail and probably leave a small "hill" of sand at the rock itself. A wet/muddy surface can get very slippery though, but that still does not make rocks move by themselves. I think wind alone does not push the rock hard enough to make the rock push mud aside. Wind can be powerful but a rock has a relatively aerodynamic shape.
Vibrations will make it much more easier for the rocks to move (try putting sand on a flat board above a speaker (if possible subwoofer) making a low bass noise). I think this is related to dynamic and static friction. The friction experienced to start moving a still object is higher than the friction of an object that is already moving. Vibrations would push the rock upwards all the time, reducing the static friction and making movements more likely. It would be interesting to setup some infrasonic and ultrasonic sound measuring equipment there. I suspect however that whoever is making that sound, does not want you peeking around (secret military facility, alien outpost, corporate zombie-making facility resident evil style, etc.).
Are there any top-view maps of rock movements over the years? It would be interesting to see if there was some sort of pattern in it.