[jogosub]

Take off the spare tire lid and check, if the spare tire is tightly secured and then re-load all tools, jack handle or anything that might bump against the spare tire rim. Also, on the left side behind rear seat side panel is pre-wired trailer hitch plug that may be hitting the body of the car. You would have to take the left rear side panel out to get to it. Also check the alignment of the rear deck/lid if it closes tight. The car body flexes and if it's not tight enough it may generate "click" sound.
Last but not least, go and look under the car and check if all bolts and nuts around rear sway bar are snug tight.

 

[jogosub]

Synchronizing properly the robotics that assemble the car in Indiana, is a tricky task. Typically, those engineers in product quality, have to re-align and re-program those quite frequently. I watched them doing it on BMW assembly lines near Munich and Saab assembly lines in Trollhattan. Unless the car is 100% hand assembled, like some expensive makes, these things will happen. Metal strip above window in the cargo area would be one of those.
However, Murphy's Law is when you bring your car to the dealer to fix it, you will not be able to duplicate the clicking sound! LOL

 

[jogosub]

It's going to be tough to duplicate the problem... but, you may luck out and they will hear it, while you are test driving the car with a technician. Good luck! Showing them, what you read here, may not help, in my opinion. They have to justify, what they do, to SOA. Otherwise they will not get warranty reimbursement from them.