I have a rattle over bumps somewhere in the rear bumper or hatch area, i did search previous threads and tightened up the stock bumpers on the hatch joint, to no avail. Wondering if anyone has heard of this, it's not the endlinks, the ball joint in the link is tight. strut is bolted tight top and bottom. it sounds like the rattle is inside the body panel(s) somewhere....

 

License plate bracket maybe? This maybe unbelievable but both of my Mini's have never had a rattle. Good luck

 

Any chance you have the deck lid lift straps detached/dangling? This silly thing stumped me for a bit. The ***** on the end of the straps would swing around over bumps and rattle against the interior plastic hatch panel.

 

try tapping the latches of the the rear fold down seats. those were also the source of my 'rattles'.