[mythtv] Jittery sound - ALSA / AC97

[Brett Buckingham]

MythTV 0.7
Mandrake 9.0
AMD Athlon 1600+, 512MB
on-board VIA 8233 (AC97) sound
ALSA 0.9
ATI TV Wonder (TV/Video in), ATI AIW Radeon (Video only)
External connection between the TV Wonder line-out and the AC97 line-in

XawTV works fine.

In MythTV, the sound is very jittery (loud ticking / interference noise over 
the sound) when I select line-in as the recording source, mute line-in, PCM 
100%, igain 100%.  Alsamixer shows a red "capture" above the capture bar.

If I mute PCM and un-mute line-in, the sound is fine, but of course then the 
sound is not synchronized with the video.

>From /etc/modules.conf:
  # On-board sound
  above snd-via8233 snd-pcm-oss
  alias sound-slot-0 snd-via8233

Any ideas?  Can't seem to find anything relevant in the mailing list archives.

Brett