I used to be biased against Western Digital due to experience back in the days where they needed wacky overlay drivers in MS DOS. Since I bought the 80GB SE drive, my opinion of them has improved a lot. They've been the top drive on StorageReview.com for a while now, as well. Unless someone can provide some actual evidence of Western Digital drives having a problem in Linux, I'm not going to consider that as a valid answer, as it really seems like biased rantings at the moment.
I'll try diabling ACPI and APIC and see what happens. It may not be a disk activity problem at all, but simply an IRQ problem. Thanks for the help.