| my experience
i had a similar problem when using my soundblaster extigy as an A/D converter while my laptop was plugged in. now i have to do all of my recording running off of battery power.
i haven't found an answer to fixing it, the only explnation i could come up with was that the audio ground, and the comuter's digital ground were interfering, and i was getting the same digital sound.
while i haven't gotten to play with sample hold oscillators too much, i can describe the sound:
there is a high pitched center to it, but it cuts out every once in a while depending on the hard drive activity and processor activity.
i assume that the audio in my extigy is being grounded through the shield on the USB cable.
i've experimented with a few USB cables, trying to ground lift them and test them with the system, didn't work. i think the real solution would be to figure out how to ground lift the USB cable, while providing a dedicated ground to the external box, but this is something i flat out haven't had the time to try yet.
-alex
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