Hi
After I superflexed my bushes, I got a knocking which was based on the lower arb link joint knocking on the wishbone when the suspension was fully unloaded. What I had to do was put 2 washers between the bracket and the subframe, where each bolt passes through it. This was because I had cut too much of the bottom of the bushing, and so it sat lower down than the factory standard one.
This might not be your issue, but it's certainly something I would check. If this isn't it, I would suspect that it is the anti roll bar that is not centred. Like boilermansab, mine only had one collet, and not two, as I think it did have originally.
I hope that this helps.