I've had this problem on my R55 Clubman 2010 for a while now and have a mechanical background. Trouble is when you stress test all the usual suspects (bushes and balljoints) with a lever bar nothing obvious shows up and it's incredibly difficult to replicate the knock when the car is motionless and jacked up. I've changed the track rod ends and drop links (mainly because they were cheap) but this hasn't cured the knock. I had another good look at the car yesterday and found that with both drop links removed I can feel play and movement in the front anti-roll bar via the bushes. With the drop links connected I can't feel this play, even with a pry-bar. I plan to change the front anti roll bar bushes for urethane ones in the next few weeks but it's going to have to go into my mates garage for this as they seem impossible to get at without lowering the subframe. I'm convinced this will cure the knock as I've ruled everything else out and it's the only place I can't feel movement that would translate into a knock on uneven road surfaces.