Why do we often hear a cracking sound when we walk pass a rubber plantation?

Answer 1

That is the rubber seed which splits open. That is the process of seed dispersal.

Answer 2

These plants grow so quickly you can actually hear them. Leaves unfurling are probably what you are hearing. Same thing happens in corn fields in summer's heat.

If the wind is blowing when you hear these cracks, could be stems or leaves bending and snapping back.

Answer 3

It is the dried fruit exploding and dropping down to the ground. You can then find the rubber seed if you search properly.