[davidmanze]

All I can say: If I use the D750 or any other Nikon on AF-C, there's always a noise and movement when I release the AF-Button and push it again. But of course, those screw-drive AF on (comparatively) cheap third party lenses are not the most precise mechanics.

It's a FW problem within the lens, maybe I'll send it in, Jolu. Remember it's the Pentax mount.

  Reverse engineering AF seems to cause quite a few problems, there are loads of complaints from those having AF accuracy problems with Sigma. One of the great things is practically all of my Nikon mount lenses are spot on and require no adjustment, on Pentax it's a story of -8;+5, -10 etc throughout the range!