Discovery 200 loud knock from front

Hi, I have had my K reg discovery for many trouble free years, recently as I was about to reverse with the steering on full right lock there was a single knock from around the front right wheel. I then drove for twenty miles, mostly straight roads ok until I turned full lock right again to drive into a parking space, this time there was much louder knocking but continuous like someone hammering underneath. A mechanic friend has checked the steering and suspension, this is all ok. Any suggestions where to look next.

Aye start looking for a better mechanic

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