Had the same problem and tried plugging into my computer that uses a three prong, plugged into a speaker, tried different outlets, different guitars, different cables, surge protectors, etc. with varying results, none of which helped in a huge way. I finally got the hum mostly under control, though! I forgot I had an old Voodoo Lab Pedal Power 2 Plus laying around. Plugged the board into the outlet on there and it seems to have kicked the hum. There's still a little noise that I wouldn't call a hum, but more like room noise I'd expect on a microphone. It's not a nuisance and I can clean it up pretty easy in recordings without squashing the guitar track with Waves x-noise or z-noise. I might only notice it because I'm more keenly listening for a hum, too. Anyway, this helps like 2 people since most people won't have a Pedal Power lying around, but it's worth noting that is a way to fix it for anyone that has one/wants to buy one.
