[Racer20]

They say it takes a big man to admit when he's wrong . . . I should have known that as soon as I categorically ruled out the steering gear that it would turn out to be exactly that. The dealer was able to pinpoint the sound as coming from the gear. Since my car is out of warranty, they tried adjusting the preload before slapping me with a $5000 bill for a new gear, and so far, the noise is 100% gone and the front end feels as tight as ever.

Apparently this isn't a BMW sanctioned repair, but it worked for now, and at least we know for sure what's clunking. He said a 17mm socket is all that was needed. You can see the mark where it was originally lined up, he turned it 3 notches. He said 4 notches was too tight and two still clunked, so he settled on three. Note that the special tool for the F30 isn't needed for this gear.