Found the cause when I'd got the Saab in the air today and one of the rose joints had a 'tiny' amount of play in it. Still they've lasted nearly
3000miles, which is about a thousand more than the balljoints lasted on it.
Scary thing was how knackered the joint was and it still felt better than the ball joints did LOL, fact that the lining fell out miles ago might not have helped either ;-)
Matt