You could try overclocking (or underclocking) the main system clock of your computer. It'll most likely be in BIOS as the front side bus frequency- try shifting it up or down 1-2% and see if that changes your radio at all. This won't eliminate the EMI, but will change the fundamental frequency and possibly shift it to a channel you don't care about. Then again, you don't know what's causing the EMI, and changing the system clock should change the ram, FSB, PCI and AGP busses, won't necessarily effect all the other components.
Double-check the case grounding, too. If it's good, try a supplemental grounding electrode of some sort, connected to a good grounding electrode with as short a cable as possible. Conventional ground wires are extra-especially lousy at dissipating ground voltages much above 60Hz since impedance at higher frequencies is so high, and if it's a long path to ground, it may just be harmonics and noise building up on the case.
