Muhahahahhahahahahah
I've just found the stuff that is causing metal sound at the rear section!
It is at the spare tire! Check if there is anything on top of your spare tire!
For mine, it was the tools the the infiniti leather bag!
Hope this will help some of you with the same problem!~

 

I make sure the tools are wedged between the spare and the trunk. I bet
those tools made quite a racket when you hit the rough roads!
Good Kill!

 

I have a "clunk" sound coming from the rear of my G, when I hit certain bumps, like where they repaved a trench or similar, I tightened my spare, the tools are just in my trunk now, and at first it seemed to stop the noise, but just today, I noticed it again. Has your noise stayed silent still?