Gotta believe that vast majority of FS knocking on Diverge and Roubaix bikes is due to misadjustment...largely because the preload on the FS is fiddly...see the video I posted on adustment and hard to get it right....or harder than conventional headsets...and too loose the thing will knock perhaps with greater sound propagation due to the complexity of FS.

All said, I wouldn't own a FS bike. If I need more front end compliance than 28c on a road bike, I would find a pre FS Diverge or equivalent.