I'm certainly well into the realms of wild speculation by now. What remains the same? The location of the computer? The power socket you're plugging it into? Presence of any environmental factors?
Your case should have good enough EMI protection if it was bought in the EU, but if you are sitting on top of a mini Chernobyl then maybe something's getting through - try a different power socket, or a different room. Heck at this point I'd be carting it round to my neighbours house just to check - a good an excuse to join the Hexus.lan as any perhaps?