Suspension 'clonking' - what's the most likely cause?

[Allroad_2013]

Our Allroad has developed over the past two or three months a 'clonking' sound which I suspect is a suspension ball joint as it appears to be emanating from underneath the car towards the front.
There appear to be three ball joints per side at the front and I'm wondering if anyone else has had this symptom and established which one was causing it? Also likely cost / complexity of doing the job myself or having dealer / specialist undertake the work?

[Crasher]

Usually it's the bottom ball joint, 4G0 407 689 C but these can be an absolute **** to get out as the steel body rots solid into the ally upright, we often have to use an induction heater to gently heat then drench with Rost Off Ice and then heat again until the come away, it can take a couple of hours. You MUST never use a gas axe on the ally as it damages it. The top nut and retaining bolt are one time only. This is an 8K A4 but it is the same part, this one came apart so easily we were surprised.

https://live.staticflickr.com/65535/51019222968_3313bd708c_o.jpg (https://flic.kr/p/2kJoRvj)