The interior plastic panels that are on the hatch are held up against the hatch with a "C"-like small clamp that is wedged in the panel. With time, these come loose, and fall out of place in the hatch, causing it to rattle incessantly.
To remedy this, remove the plastic panels on the inside of the hatch, and replace the metal clips that have fallen out (or see if you can re-use the same ones, but make sure they don't fall out again when you re-install the panels).
Good luck!