Persistent 'clunk' coming from the PS rear

[SBSerpent]

I have a BDR 2011 build with the BMW rear end (IRS with separate springs and shocks). On aggressive low speed cornering, I hear a 'clunk' coming from the PS rear while turning right. Again, this only occurs when the turn is aggressive and at relatively low speed (~30 - 40 MPH). I've gone underneath to confirm that all bolts are tight and that all bushings are in good shape. The shocks are bolted securely to the frame.

One thing that I cannot check is the upper spring mount to the frame. I can't see anything with the wheel off while conducting an inspection through the wheel well. I've tried going into the trunk to see if I can find some sort of mount that secures the upper shock to the frame. Nothing that I can find that is accessible for viewing the mounting. This is the only thing that I haven't been able to confirm out of all the rear suspension and drive train components.

And yes, I have checked the 14mm bolt that secures the diff to the sub frame. All good there.