Just a couple of thoughts on this, firstly regarding drop-link length, secondly the knocking noise.
Changing the length of the drop links may alter the effect of the anti-roll bar rate, it's a trick employed on track cars to set up handling, not sure which way it goes, if longer makes the car stiffer or softer, just came across that little snippet in a Ford specialist magazine.
The other thing is the ARB itself, they have been known to move sideways and catch other suspension parts, there should be signs of contact if this has been the case.