Check if there is any (lateral) play between the spring and the spring seat. When you are turning the wheel lock to lock, do you hear any sound (you have to put your ear inside the wheel arch to check)?
When I changed the OEM springs with B6 Bilsteins (after 40k km the OEM were knackered...) it developed a strange knocking sound at the front. The Bilsteins are reverse dampers with embedded bump stops (at the front), which means I had to take out the existing bump stops to fit them. As a result, the car stood about 1-2mm higher than previously - this height difference was enough to cause the spring's first coil winding to slightly end outside the spring seat, causing a tiny bit of lateral play. I wish I could explain it better - apologies for my English.
You can also easily test that by grabbing the spring and pushing it back / forward hard. This is a noise that typically gets worse the more you drive...
Other than that, I can't really think of something else and what I wrote above is a really long shot... When you changed top mounts you said that the
problem was 100% solved, but then it reappeared. To me this indicates that there is some give / looseness in the system. Once everything is tightened up all is OK, but then over time it starts to become loose again.
I have the ElsaWin package, so if you want pm me and I will send you pdf extracts of the suspension parts and layout in 3D (unfortunately not enough posts yet so I can't upload a picture).