Intel boards tend to like Radeons over nVidia products, so I doubt the problem is that. I’m definitely for EMI. Unlike the newer XT cards, the drivers don’t have a recovery function, so any EMI is multiplied by time, and rebooting (resetting the card completely) will solve this. The newer drivers many have solutions for this, or try moving any flourescent lamps, fans, clock radios, speakers, etc away from your case, and if that doesn’t work try some aluminum voil on the sides if your case is Al (doesn’t work if you have a steel case, steel works far better than Al for EMI insulation). And make sure you leave the sides on. If you have a window, try and cover it with some Reynolds. This all should help reduce EMI.