Audio Subpar Using Firewire?

A newbie here, and I need your expert help, please. I recently bought an HC96 and taped my daughter's voice recital. I captured the video on my PC using a USB cable and, as expected, got really mediocre video quality but surprisingly good audio quality. I went out and bought a firewire cable today and tried capturing it again. The video looks much better, but the sound is very "tin-y" on higher pitches, almost like the the speakers are a little distorted.
Has anyone else experienced this? Any ideas?
Many, many thanks.

record in 16bit mode, not in 12bit.
dont use easy-camera-modus - it only records in 12 bit.

Thanks Peter. I guess that's for "next time," right? Nothing that can be done to fix this tape?
Thanks again.

maybe. you wrote you got better audio quality with usb and better video quality with firewire - so join both in one file. i never noticed this but will test it.
some audio-editors allow you to remove the noise.