I have a 405 J reg (91) 2 litre 150,000 on clock. On start up, the steering is not a problem but after 10 miles or so, the steering feels light,(drifting) and when I trun the wheel hard knocking sound can be heard coming from the front; but this seems to go when I straighten up! When it gets bad, the steering wheel rudders just like I have a flat tyre. Any ideas on the most likely cause?? Thanks....