Sound is frequently out of sync with the picture, on all sources that I have used (inbuilt freeview, external Samsung DVD player, set-top box).
There is no way to adjust the sound delay, unless external sound amplification is used.
However the problem is that it happens to different degrees depending on channels and source, and varies during watching - in some cases it has got hugely worse over 30-60 minutes of watching. So one global setting will not fix the problem.
I contacted Samsung and they are aware that it is a problem with this model of TV, advising me to return the TV, and Currys Knowhow tell me that it is an issue with some of the Samsung F series TVs. This is my 3rd Samsung TV in 3 weeks, the first two being 6400's, both of which had the same problem.
I had hoped that upgrading to a 6670 would be the solution, but unfortunately not, so I am returning the TV.
...and I am giving up with Samsung TVs altogether.