Xantia Steering Shimmy Rattle Scittle Shake

[ajfphil]

Xantia 1.9td auto
55k
When you drive at any speed over a series of closely road irregularities, like tree roots or frost damaged tarmac steering wheel kicks back and shimmys.
Speedbumps bigger irregularities fine
If this was a landrover you'd fit a steering damper, closest other example I can think of is the scuttle shake you'd get in Triumph Spitfires as the body flexed.
Have fitted new droplinks but problem persists - ride heights ok and on standard tyres and wheels 205/60/15
Have had ball joints track rod ends and bushes checked by 2 independant Citroen garages who say these all fine.
This is my 3rd Xantia and this isn't normal behavior
Any ideas please ?
I did wonder if it could be worn anti roll bar bushes and the roll bar oscillating over these type bumps.