DVDSubEdit will find them without fail and very quickly, just put a check in the box for "Only show forced subpics"; if the video window stays blank, there are no forced subs. If some show up, use the stream selection box to see which stream you need to include and whether you need to check "display only forced" in DVDFab Ripper. Again, onoce they are rendered into the video in the MP4 conversion you can't remove them.