Interesting questions bigshot. As it might be semi-related could I point you clever lot at this thread http://www.head-fi.org/t/620094/dropouts-in-foobar-over-spdif-with-boinc-and-eist-solved
In short, I used to run intensive computing progs in the background while listening to music through an Asus DX -> CA Dacmagic. Occasionally you'd hear very tiny clicks, but they were so quiet and brief as to be ignorable and I didn't realise it was a problem. Then I swapped the DX out for an M-Audio 2496 and it was terrible! Clicks more frequent and more disruptive to the music. However with BOINC switched off and speedstep disabled it was fine. Recently I've been using an AMB gamma2 (gone back to the DX) and it must be far more robust (it has a clever asynchronous something-or-other) as it seems to be immune to any of these problems regardless of what else is running.
So what were these noises I was hearing? Perhaps they were this mysterious "jitter" caught in the act? Or buffer under runs? You can try the same thing yourself using a cpu stress test - something like prime95, Intel Burn Test, or LinX, and listen out.