I have seen this on loads of DVD player/PJ combinations.
The only thing that removed it for me was switching to a progressive DVD player, which ironically is the Sony 730.
I am quite sure it is something to do with the interlaced pciture and its line count.
However, if you are experiencing the line which i think is situated just below the 2:35:1 black top bar from your description, with a progressive machine then I am not sure how you would remove it.
Can anyone else help?
Cap