I would agree with Cutterfilm (above). It looks like there are two camps: those who believe that a DAC puts out varying information depending on whether it is vibrating and those who believe its information rate remains the same until the point of data failure (so much vibration that the buffer cannot put anything out and it skips or stops).
On the issue of "jitter":
Jitter, from my understanding, has to do with the master clock reading those 1s and 0s. I think master clocks come in varying degrees of quality and, therefore, accuracy. The better your clock, the better your DAC, and the better your sound should be to you.
However, the master clock's performance should not be predicated on whether it is vibrating or not. Perhaps massive amounts of vibration would cause a master clock to not function properly, but that should equate to a data error not differences in sound quality.
Again, you close your eyes and listen while a friend blows on your stylus or taps your turntable in the right way--you'll hear it. Close your eyes and have a friend shake your hard drive. Do a double blind test. Repeat. It's not going to matter until the point of data error (where the DAC cannot send out data at all or it cannot buffer enough data during the non-shaking times to give you an audible sound--ie skipping).
In short, I really believe that you'd be better off spending more money on better digital components than trying to isolate the ones you have if your goal is to improve your sound. My rule of thumb would be: computer digital source is not going to sound any better by doing anything to it.
I've never seen any white paper reports indicating that vibration leads to a computer reading less binary information off of a hardrive. That is the real issue.
A third point of view: Where you stand depends on where you sit--I suppose. Those who've invested a lot of money into vibration control for a computer hard drive need to hear it as sounding better. Those of us who didn't spend the money have to say it doesn't.
