Its a common fault, the plastic guides in the shocks perish, shrink and then they rattle and nock.
You could try uprated kyb's, AGX's to be exact or coilovers. My dads got tein super street coilovers on and they are very good for the road, not too hard and not too soft.
summit like this,
http://shop.scoobyclinic.com/index.php?route=product/product&path=63_163&product_id=553
assuming correct fitment of course