its on a 680i C2D setup.
I thought it was the speakers (Z-5400) and creative relaced them for me (had a few other issues too) but it hasnt been solved. Its like a low thump at random intervals.
Its quite well documented across lots of different platforms, currently most agree its due to a total lack of EMI shielding, something all manufacturers other than Asus are guilty of at the moment.
Anyway, I dont own the PCI-E one, im only going off the reports in the Sound forum. Certainly if Vista is going on this new machine then DirectSound EAX is less of a consideration anyway, EAX wont die as a concept but it will be implemented through OpenAL from now on, the branding itself might dissapear also, really depends whether Creative want to kill EAX or not.