[Myles O'Reilly]"This has never happened to me as I always shoot in PAL 25fps 1080p. "
There is the problem.
I guess that you'r default Sequence Setting is PAL.
FC has a bug and when you import audio files, FC treat those files as they would have the time-base of your default Sequence.
Having your default sequence PAL, when you bring the audio files to an NTSC sequence, the audio gets out of sync.
Your workaround is not difficult:
- Delete the audio files from FC (Browser, sequences).
- Set any default sequence with a 59,94 fps.
- Reimport the audio.
that should work.
If you want to learn more about the bug and how to fix it in other situations, read this: http://library.creativecow.net/lyon_matt/fixing-fcp-assets/1