Mine too!!!!!!!...........sounds like boot area, but mine is coming from offside damper / spring area (top of), so resonates through boot area.
To check, gently rock the car from the nearside corner of body, not up & down, but push the body. Mine then starts to `click`...........very annoying, although sometimes the `click` is there & sometimes not. I am guessing something is not sitting right somewhere & goes out of line every now & then.........or an internal defect in the damper