knocking noise

[samscsy]

hi all, ive got a freelander 2002 serengeti petrol. there has been this knocking noise when i turn the steering wheel right, but only knocks when i go over rough ground.. its wierd as when the car is on a straight and ive taken it ove rough ground it doesnt knock. also my steering wheel is off (isnt straigh). ive taken it into a land rover specialist who has looked at all the bearings and bushes and said they are all fine, and he doesnt no where the noise is coming from. didnt have much faith in this diagnosis!! any ideas thanx