Anyone find a definitive solution to this issue.

Do the cradle up tighter.

In the sedans the rear vent below the tail light needs glueing  down, remove the side trim & discover how it's only held on by 2 plastic clips (I think they intended for the trim to push up against it to stop it rattling )

This clunking noise ( I think rear left but sometimes sound like it's from the front-always left side though- going over smallish sharp bumps and usually just after turning left) is driving me nuts. I have had Ford look over the car 3 times, initially they pointed the aftermarket suspension. Got the suspension shop to investigate a further 3 times-can't find any issues. Had the shocks returned to Bilstein for testing no issue found. Took the car to Pedders-they spent a good couple of hours going over the car- they could not find a fault. But the clunking continues. Took the car back to Ford and they agreed to replace the diff- still no better. WTF!! Any ideas-pulling my hair out. 

without knowing exactly where the clunk is coming from, it's almost impossible to diagnose, especially over the internet.

 

Did the suspension shop at least manage to replicate the noise and find out where it's specifically coming from?

The suspension shop was unable to replicate the noise. However, while Pedders had the car we got it to clunk once, but it was not as obvious as usual. Sometimes it sounds like something hitting the bottom of the car-really loud but other times a bit softer. I starting to think it may be from the left front- but no one can find the issue. All of the bushes and links have been checked and seem okay-so I grasping at straws.

if it happens often enough to be annoying, then you'd have a location/situation/environment that you can replicate it in?

I have tried many times to replicate the noise but it does not alway happen. It always seems to happen innocuously. I usually hear it (when it happens) just after turning left, start to accelerate and hit a couple a small bumps. I would only be travelling around 40 to 50km. When I hear the noise, I have tried turning the car around and going over the exact same piece of road -sometimes I can replicate the noise -other times I cannot.

well, I think you're going to be chasing ghosts, so to speak, until you find a way to replicate the issue without fail...

 

you might need to take somebody in WA who knows what they're doing with these cars ( @Ralph Wiggum comes to mind) for a drive to get them to listen to it in person to give you some advice.

 

or if you can replicate it, take a video a few times over and post it on YT ad link it here so we can all have a guess at pointing you in the right direction, at least.

Here is a fix done to my car before I bought it. It's worth a look.