Noise when going over speedbumps

Whenever I go over speedbumps about 15mph or more, I hear a 'clunk' sound from the trunk. I suspected the black storage tray or bin, underneath the trunk floor cover panel, was popping up and making this noise.
So I took this bin off the car and test drove over the speedbumps. The 'clunk' sound was eliminated.
There is nothing to hold the bin down except the floor cover panel which does not seem to hold it down very firmly around all edges. I guess when there is heavy item or luggage put in the trunk, this storage bin would not popped up when running over speedbumps, but I have not tried yet.
Have anyone experienced this and have a fix for it ? Perhaps the latches on the cover need adjusment ?
Is this a design flaw or just my car only ? The car is less than one month old.