The wider the candle, the greater the volume on that bar. The volume comes in at very distinct technical levels – more often then not at highs or lows, breakouts of small consolidations and reversals of previous heavy volume bars. In my opinion this is automated as I know people who have automated strategies on breakouts from small patterns in the tick charts. Automated trade management functions are then overlaid. These algos tend to be used in very noisy markets and probably exacerbate the noise levels by causing small price overshoots on the swings.