Has anyone experienced excessive tramlining with part worn Continentals (standard size) front and rear?

I have had the suspension set up done by OPC and am happy that tyre pressures etc are fine and when the tyres were new I had no probs. The old Michelin MXXX3 tyres displayed no problems but now with 50% to go on front and 70% on rears the nose has started to follow uneven tarmac.

Any ideas?

Andy
87 S4 Euro Auto (with new t/tube!)