Danny,
I have dealt with this issue before. While I was not shooting in HD, I was shooting on the XH-A1. I don’t think HD is the issue–it’s how Quicktime and FCP deal with 24f-(23.98). Is there audio sync slip just in FCP, but not when you open the captured file in Quicktime directly from your capture scratch on your hard drive?
Or is the file out of sync in the viwer, the canvas, and in Quicktime proper?
Check:
Do not open FCP
Open your movie file directly from your hard drive.
It should open automatically in Quicktime.
If this file plays back correctly, but it has audio sync slippage in FCP, then here is the work-around I have used:
open file in QT
export:options:settings
settings:
frame rate: custom 23.98
compressor type: DvDVCPRO-ntsc
scan mode: progressive
aspect ratio: 16:9
uncheck internet streaming
quality at BEST
Hope this serves you.