I keep hearing this rattle in the rear and couldn't find the culprit until I realized it was that the upper tailgate wasn't latched on the left side. Now, my upper tailgate is not is great shape (should have bought Paul Grant's

) but it does unlatch and latch. I have pressed the particular side down to latch it, but it comes unlatched after a few miles and the rattle comes back.
Does anyone know of a way to keep the latch latched? Do I need to adjust the tab on the body? I did a search and couldn't find anything. Any help would be appreciated. TIA!