I've have been dealing with this issue since day dot.
1. Heard the knock shortly after purchase, got checked and was told struts. Bilstein's replaced all round. (new)
2. Knock came back 2 weeks later. Just accepted it was "Bilstein" knock till recently.
3. Got jack of it and took the car to be inspected at a new place. (Subaru Experienced Shop). They straight away said it was struts. I said it's not as they are new.
They tightened everything and in the process snapped a stud on the passenger front strut top.
They replaced it!
4. The shop had a Bilstein Australia Rep there one day and they asked him about it and he advised the "slide bearing" issue. They got the bearings sent down and fitted them. No difference. Knock still present.
5. Upon returning from a weekend away, I hit some road kill on the side of the road and seized the passenger side front Bilstein.
6. Contacted Bilstein and got a replacement front set sent and they were fitted up and was good for about 3 days and then the knock came back
7. As the car was there, a Rep from a tuning shop mentioned that it has an aftermarket front swaybar (Whiteline) it may have a knock from the nolathane bushes.... Yet to see what they are going to do about this as the knock disappears in the wet weather and I haven't had a chance to go back yet. I've read about this, just not sure what the fix is?