I am not sure what a cast just before the ball is,sounds like pronation as described by Hogan,but be aware of over analysis.You are clearly a competent golfer and when my game slips I go to the pro who sorts it straight away.In your case it could be something as simple as your rythym is out,it could be anything.Best place for swing sequense for me is here
http://www.golfdigest.com/instruction/swingsequences/
you need to register but its free