xantia knocking front end?

my 95 xantia knocks and rattles form front end today! (all ball joints bushes mountings drive shafts etc are fine passes mot ok) tomorrow runs smooth and silent! next day! who knows? seems to have a mind of its own. Recent spheres fitted, fluid level fine, no leaks, ride height ok, goes up goes down when required, just rattles and knocks loudly from time to time seemingly for no reason moving ride height lever seems to help hardly a cure though