I have a Fiesta Zetec with a 1.4 TCI engine. I have had this car since 2010 and until early this year I have had no problems.
A knock started to appear when I turned the steering in either direction. The vehicle was taken to both a Ford garage and an indepndent garage but despite changing the tie bar links the knock was still present, and after the vehicle had been lifted off its wheels the knock was more excessive.
I discovered the cause of the problem and have informed both garages of what I had discovered. By unlocking the steering wheen height adjuster and lowering the steering wheel by a very small amount (5mm) the knock has been resolved.