Hello Folks,

I've had it for ages, sounds metallic like a loose seatbelt assembly. Actually, it
comes from the LED array for the brake light in the rear window.

Cure:
Remove the two screw covers, and the screws of the brake light housing.
Gently tease away the assembly. Beware, there are 2 "suicide clips", which
will need replacing if you break them!

Undo the 3 torx screws that hold the LED array. Apply a strip of female
sticky-backed velcro to the array, noting that you'll need to remove a notch
for one of the locating pins. Attach some male velcro strip to the female,
noting the notch, and insert the array back into the housing.

Re-attach the housing to the car, ensuring that the bit which shows in the
back window is thoroughly clean. Rattle be gone!!

Regards,
Steve