The ARB end.
It's not that they don't fit they do. Basically the bolt that goes through the ARB hole is slightly too thin. But it is not thin enough to fit a poly sleeve over to stop the noise. I tried everything from plastic sheathing, heat shrink, amalgam tape etc. No matter how much I tightened them I couldn't stop it.
Maybe it was just my Eibach bars but the noise annoyed me so I took them off. It must have been bad as even the wife said without me saying anything "what's the knocking noise?"
Try them and see what you think. Like I said it may have just been the eibach bars. But when I put the OEM ones back on the noise stopped.