Ford Mondeo 2008 steering clunk?

My Ford Mondeo 2008 2.3 Auto Station Wagon (98000 km) has started to make a clunk noise (feels like a clunk rather than makes a noise) when I turn the steering wheel left or right about an inch. This only happens at a stand still or at very low speeds. I have checked the power steering fluid level, leaks around the power steering unit, CV joints.