Ibook Audio Puzzlment, strange audio problems on G4 ibook Options

[willm]

Hello all

I have a strange audio problem that I can't resolve.

I have a G4 1.33Ghz iBook running OSX 10.4.9. 

Weird: Audio skips or is distorted in if playing through either the internal headphone socket or my firewire audio device (an M-Audio Firewire Audiophile) but not if playing through the onboard speakers. The distortion is not fuzz - it's hissy, squelchy and intermittent, almost as if the sound were being played through an effect (though not one I'd ever want to use). I get this with iTunes (CD and mp3), with playback through the Finder, and with Peak.

Weirder and weirder: when I use Logic Express with the Firewire audio device or the internal headphone socket the sounds do not distort. However, certain individual sounds - ie specific samples or tracks - within songs don't play. When I playback through the internal speakers these sounds do play.

What I've done so far:
• run repairs in disk utility
• reinstalled Tiger and updates
• reinstalled the latest M-Audio driver
• junked Quicktime and iTunes prefs
• checked that audio output is set to 44.1

Does anyone have any further suggestions?

Thanks and best wishes
willm