I don't know. But if one large trader makes a big move (say for logical reasons like a serious investor acquiring large stake) then it may be followed by 100s of other traders who try to decipher what he/she meant, each making different conclusions and decisions, some shorting, some going long, and each setting different targets and stops. They all have reasons to do that, each feeling some purpose and enlightenment, but collectively they pull the market in different directions that causes lots of fluctuations without any one trader's logic prevailing. Whether that can be called random or not, or noise or not, may be a topic on its own (and maybe that's what's being discussed here).