is it new? maybe just needs some lovin'
my 24-70 would stick at 28 for the first month (almost took it back because of it). But it was so darn sharp, i figured i could live with the required extra bit of force needed to get from 28 to 24... but at some point, it just "worked right" . Can recall when that stated to work right... only can tell you after much use, it doesn't stick anymore
stick might not be the best description, the ring turns but the focus doesn't change...sometimes and only briefly. I can live with it as I prefer generally to set magnification then move in and out to get focus or just use the very efficient AF. Out of warranty anyway but wondered if this was a common problem.