Rattle on bumpy Roads, out of ideas

[RichRS6]

Did you ever get to the bottom of this issue ?

Probably a different sort of rattle but I had a noise in my C5 that really annoyed me, heard it every time I went over a bump, during acceleration or braking.
Traced it to one of the rear doors, took the interior panel off but there was nothing in the bottom of the door itself.

Gave the panel a good shake and turned out to be a 10p piece that had dropped into gap behind one of the rear door mounted ashtrays, not in the ashtray itself and not visible if you removed the ashtray interior, I had to remove the part that the ashtray sits in to get to it.

[yorkrs6+]

Yes - passenger side lower arm, causing the knocking.