Explain this in physical terms?

I jump from a wooden floor straight up to a certain height and fall down, the impact against the floor causing a slight noise. I jump again to the same height and fall down, this time extending my legs as I hit the ground. The impact causes a much greater noise, noticeably shaking the room. I do not noticeably bound upward either time. How is it that my actions from within freefall seem to generate force?