I recently bought a 2007 BMW X3 M Sport from a BMW dealer. The car was sold to me with non-BMW approved tyres fitted, although they were of correct size and profile. There were knocks and clunks when pulling away or turning at junctions and also in reverse. They eventually changed the tyres but the noises persist, though reduced.

I'm worried about damage to the drivetrain caused by the mix of tyres. There have been other faults they seem not to want to fix. The car has been back four times but they say that they cannot find a fault. I want rid of the car now as I've had four months' stress and wasted time. Where do I stand?