DVD - MPEG2 PICtURE LOOKS GREAT - BUT AIFF SOUND OUT OF SYNC?

Have edited a 10 minute film (Shot on DV25) in Final Cut Pro 4.
My machine is few years old - 466MGhz - G4 with 1.5GB of ram.

The job includes several picture layers ( picture in picture) and captions -

It plays perfectly in FCP and exports fine - via fire wire to a capture deck - and the resulting MiniDV tape is good.

However - when I attempt to export this via "Compressor" version 1 ( integral with DVD studio pro) to make MPEG2 the voice sync slips out by at least 6 frames by the end of the film ( only 10 minutes)

Settings -

DVD PCM Audio -AIFF 48Khz,16bit stereo
MPEG-2 60min High Quality Encode 7Mbps,2-PassVBR,4:3.

I'm new to DVD - but have followed steps outlines in " Final Cut Pro 4" by Diana Weynand -( and spent ages reading help files-) faithfully . Also tried the gamut of possible settings

As job takes over 2.5 hours to compress- am tearing my hair out .

If anyone has any suggestions I would be very grateful.
Joe

London United Kingdom.