To be honest, I haven't really attempted to earth my gear (it's already earthed - here in UK we still have three-pin fused plugs), since many others have tried following the manual's workarounds, without much success from what I've read. Everything runs off a single power point in star formation, & even taking the laptop & softstep into another room on their own, the problem's the same.
True, if I'm touching the guitar strings/bridge etc the interference goes away, & it's greatest while hovering my foot close to the SS (my body's acting as a kind of aerial or amplifier), but I don't have this sort of problem with any of my other gear/set up, & there's a lot of it. The only similar trouble I ever had was when I had a CRT monitor; very similar sound picked up by the guitar. I now sit in front of 2 LCD monitors & a Macbook, mixer, FX boxes, 4 delay/loopers, ADAT interface......nothing. 'Til that backlight comes on.
I'm thinking maybe I'll leave the light off & get a pot of fluorescent paint....:)