Pulsing usually means the camera has defaulted to CDAF. One way to get this to happen all the time is to stop the lens down. Past F/8, I believe. Otherwise, it usually means the camera is struggling with PDAF So it goes back to purely visual confirmation of focus, CDAF, which requires pulsing to compare in and out of focus. Now the question is, why is this happening? As said above, most likely it's a firmware issue, since the III should be noticeably better than the II in AF.