Long story - so bear with me (also posted in FCP forum):
I edited a short film 2 months ago which was just accepted into a festival - requiring me to bring up the old project and fix some grades and lay in a new audio master from the sound designer. I did the original edit and grade on FCP2 - and have since updated to FCP3.
In the meantime I've been editing a feature shot-on-RED and had to uninstall all my Kona 3 drivers as they were affecting the framerate playback in FCP.
Now to fix the short film I've reinstalled the new Kona 3 version 7.0 drivers. I've laid in the new audio track and for no apparent reason the sync gradually slips over the course of the 17minute film until by the end it is several seconds out.
Here's the kicker - the original audio mixdown from the sound designer is in perfect sync (after reimporting it and dropping it into the timeline). And if I stack the new and the old files on top of each other in the timeline and turn on Audio Waveform display they are PERFECTLY aligned the entire way. But if you play them - you gradually hear the new track delaying more and more as the film plays. So it seems to be a playback issue rather than a problem with the file. Although I tried exporting the whole sequence to a Quicktime and it's still got the same sync problem (in Sync at the start but way out by the end). I've also tried a myriad of Audio/Video settings combinations but to no avail.
Also, when I drop the new audio file in it has a green 'render-me' bar on the clip itself in the timeline. The audio file is a WAV - but I've tried converting that to AIFF via Quicktime and the issue is the same.
Workstation config is as follows:
2 x 3.2ghz Quad Core
Dual 4gb fibre-attached to XSan2 volume (20tb (usable) promise RAID storage pool - currently getting 250MB/s avg read)
Kona3 with version 7.0 driver
2 x 30" cinema display
JVC 24" broadcast LCD
Project settings as follows:
RED Anamorphic - converted via Monkey Extract to 2048x1080 DPX (with aspect ratio padding) and graded in Color then output to 2048x1080 AJA 10bit RGB codec and sent back to FCP
audio - tried both 16bit48khz and 24bit96khz (received both from sound designer) - same issue.