Rattling noise from rear end

No, can't say that I've heard that.

Not sure what you mean by "cargo liner." Mine has a movable floor in the trunk area. I can keep it in the higher position and have storage underneath, or I can move it to the lower position, just above the spare tire, giving me more storage volume above. It shouldn't rattle in either position, but the fact that it is movable means it might not be properly seated. You could give that a try.

Good luck!

Yes, that's the same component I was talking about. I didn't know what it was called. It's probably just not seated correctly. Can you jiggle it around to settle it down? Or maybe you need to add some rubber padding in the gap to make it fit tighter? Or maybe it will be quieter if you install it in the lower position.