In Dying Light, what do the tiny white bouncing arrows indicate in the mini-map?

Every so often, I see tiny white arrows in the mini-map that bounce up and down a little. I'm almost done with the game and never did figure out what they represent. At first I thought they might indicate a horde, because they usually show up in a group of four or five arrows, but that doesn't seem to be it.

Solution 1:

Arrows are used to indicate difference in height between character and object.

E.g. look on picture below. This arrows indicate that traps are lower than character.

And here white arrows show, that shop, bad etc are on higher floor.

If those are not arrows you mean, please, provide screenshot.