Same thing here. I was hearing a rattling sound that was driving me crazy which led me to this post and sure enough it was a loose driver side spoiler nut - actually the nut came off the bolt and was rattling around inside the black plastic cover; the passenger side nut was still firmly attached to the bolt as were the 2 center nuts under the long black plastic trim piece.Today, I have looked at my rear spoiler(I remember, somebody pointed out a couple of days ago, about this noise coming from the back, but I can't find that thread), because I was hearing some weird noises coming from the rear.
I have removed the two rubber plugs, behind the spoiler and to my surprise, on the left side, the nut it was gone, I couldn't find it and on the right it was loose, I could turn it with my fingers.
I would suggest to everybody, to look at your spoilers.
My 2 black plastic triangular outside spoiler inserts are still loose so will try the double sided tape trick to see if that will stop the noise as well.
Reposting these member pics for convenience:
TSB for rear hatch alignment: https://redirect.viglink.com/?forma...ww.rx8club.com/attachments/g...-over-bump-pdf