S60R suspension problem

[irr7]

I have a 2004 S60R.
I am experiencing a loud single thump noise coming from the left rear suspension area, (shocker/s).
After having the car diagnosed with shocker, shocker bushings, sensor replacement and suspension module, (SUM), all of which I have replaced with new and at considerable cost, I still have the problem.
It's a very loud single thump noise which sounds like someone has dropped a large heavy suitcase into the trunk or if someone has just slammed the trunk down.
This only happens when I have driven over a bump, (not the pot hole variety), and then only when the car settles back down after the crest of the bump and at slow to moderate speed.
Volvo dealership local to me and an independant, (Volvo trained), service shop have spent much time and cost me much money trying to find this problem but haved failed each and every time.
Any one have any ideas?
Thanks.
IanR