Hi, Cdinkha,
Please try following to fix your problem:
1. Please click the round green icon button with a check mark at the right top corner of the DVDFab screen, open "Common Settings" window, click on "write", change the write speed as 2x;
2. Use other Blu-ray DVDs to see if this is a universal problem, or just for this one;
3. Use another audio channel to have a try;
4. You'd better copy the movie to your HDD as ISO file first and play it on your PC with software player to check if you get the AV out of sync problem, if not, then burn the ISO file to the blank disc.
If all above fail to work, plaese do as AGJ mentions, post your log here for troubleshooting.
Sincerely Yours
Malcolm Wang