997 GTS - what's rattling in my cabin?

[13m]

I've been delighted with how non-rattly my GTS is... until today. This afternoon, something has started rattling / buzzing when I am on anything but the smoothest road surface. It's coming from the passenger dash area.

Immediately before the rattle started, I opened and closed the door, opened and closed the glove box and closed the right-hand cup holder.

I may have to enlist wifey to rattle spot, but are there any "usual suspects" in the area described?

[13m]

I hope I am not speaking too soon, but it seems to have gone.

It was either:

1. The rear view mirror, which did have a buzz as I tapped it but which quietened down with a squeeze.

2. The passenger seat which was a long way back.