For about seven years, we heard a slide-clunk noise when starting or stopping.
The noise seemed to come from somewhere in the lockers behind the passenger seat. We'd hear it every time, then not at all for a few weeks. Then it would return.
I spend ages trying to track it down, completely unsuccessfully.
Then late last year, I was doing some work under the hob. To do that, I cleared out the drawers and moved the heating ducts.
And there it was: right at the back, behind the pipes and ducts: half a dinner plate.
It was well hidden, wedged in, but able to slide backwards and forwards in its hiding place. No-where near where the sound seemed to come from.
On the other hand, a couple of years ago, we were in France and could hear a Clunk noise from somewhere in the back when we went round a corner. Looked all over for anything loose, in the wardrobe, in the shower, in the boot. Nothing.
It turned out to be a loose nut on one of the end fittings of the DeDion bar in the back suspension.
Once again, not where the noise had seemed to come from.