Hi Ferret1979, re your Scenic Alize
I too have had the clonk/rattle (see an earlier post) and I finally (recently) found the cure!
I too have had changes to rear dampers (which didn't cure the problem).
Recently, and following GFB's previous posting, I took my dampers off yet again.
When checking "very" thoroughly I found that although the bottom bolts were done up tight (and to torque) they were actually not tight enough against the bush at the bottom of the damper.
The reason being that the bolts did not go far enough into their threaded hole. I found that although I could see through the threaded hole (toward the disc), the thread did not go all the way through and the bolt was actually bottoming out before applying sufficient pressure against the damper's bush.
And, if your bolts are like mine, the unthreaded part is actually thinner than the hole through the damper's bush - consequently, if the bolt is not done up tight enough, the suspension moves (with the bolt attached securely) but until the slack is taken up the damper doesn't compress and we have a clonk/rattle which even on a fairly smooth road gives a constant jiggle/rattle/clonk.
If you should need new dampers I bought Bilstein gas dampers from Euro Car Parts and, more recently, Monroe gas dampers from www.proven-products.co.uk
(in Devon). The Monroe dampers are on now and fine.
Hope this helps you cure your problem.