The symptom described does NOT necessarily mean that the outlets are not properly grounded. It could be MANY things:
A short in the pickup, or guitar wiring.
Ground loops causing eddy currents etc. in the rack (most common issue)
Short in one of the cords.
Shorts in a piece of gear
and more...
First thing to trouble shoot is to reduce variables:
1) Does it happen with more than one guitar? No - fix ground/short/shielding in guitar Yes - go to 2
2) Try several cables (and cable(s) between amp and speaker), does it happen with all of them? No - toss the offending cable(s). Yes - go to 3
3) Plug the guitar via ONE cable into a guitar amplifier with a THREE PIN power plug. Still happening? Yes - if amp has a polarity reverse switch (not the same as a ground lift, though often one switch does both with lift in the center position) - try that. Still happening: house wiring issue. No - go to 4
4) Pull the axe-FX out of your rack, take whatever you're using as an amplifier out of your rack (skip if using active speakers). Put both and your speaker on a non-conductive surface, like a bed, and make sure they're not touching each other. Plug them both into the SAME power strip (three prong, of course). Plug that power strip in. Connect to your speaker. Turn it on. Still happening? With more than one guitar and cable? Yes - house wiring or short in Axe-FX or Amplifier No - go to 5
5) Buy Humfrees. Reinstall all of your gear into your rack using them. Plug EVERYTHING in that rack, with 3 Prong Plugs, into ONE power strip and plug that into a grounded outlet. Connect your amp to your speaker. Turn it on. Stil happening? Yes - something in that rack has a short, or somewhere in that rack, a unit's chassis is contacting the rails. Try ABS/Nylon screws with the Humfrees if you need to. No? be happy.
I'm sure there are a few more possibilities, but you get the idea - break down the problem by a) checking swappable gear (guitars, cords) b) reducing variables.
Good luck.
P.S. IMHO - Furmans suck. There are better alternatives. I am looking into a Balanced AC Power unit for my rack - that is the BEST possible solution.
*** THIS BOOK *** has lots of good advice. He and I built my first studio together, way back in 1985, and he knows his stuff.
