Comment 4 for bug 399240

I have had this similar problem since 8.04, 8.10 and 9.04 also experience the same issues.
The problem arises when the graphics card is active and disk access is performed.
I have tried nvidia-glx 180, 173, but not 96 or 71.
Disabling the nvidia module makes the problem go away.

The main suspect is the fact that ahci and nvidia share the same interrupt, seen here from /proc/interrupts on my machine.
 16: 6514 6483 IO-APIC-fasteoi ahci, uhci_hcd:usb3, ohci1394, nvidia

It seems to be restricted to Asus platforms, as no one else seems to have the same problem.

Platform: Asus G2S, nVidia GeForce 8600M GT

Thanks
ecks