Thanks @SamPNW
I did the same thing by sitting in the 3rd row to find the source and noticed it was coming from the power outlet cover.
It was slightly loose, and the noise went away after I closed it.
...
Side note about finding the source of noise: I opened the upper access panel...
Hi @SamPNW, have you found the issue where it came from, and have you gotten it fixed?
I also discovered this, almost exactly the same rattling sound from the tailgate on my 2023 R1S, also Quad.
Thanks!