I'll raise the peace flag on this one. Those Monster Power conditioners aren't the "cure-all" they claim to be. No conditioner is. Yes, they help, but they don't fix everything. I wouldn't suspect the conditioner is your culprit, but obviously it's not stopping whatever is.
Per my own thoughts and another EE I just consulted:
The fact your mic doesn't give you any problems tells you it's the magnets in the pups. The strings are big antennae and they're picking up noise from something. You need to systematically take everything out of the equation.
Are you using a Desktop or Laptop? Do you have another computer you can use?
The power supply in your computer is a likely suspect.
Are your lights flourescent? If so they may be using solid state ballists. This could be a potential culprit.
I highly doubt it's your monitor.
Wireless is up in the Gigahertz. Highly doubt it has anything to do with it.
I would shut everything off in the entire house to effectively troubleshoot though. And I mean everything - Heat, AC, Wireless, Router, Cable Box, Lights, Monitors, Microwave, The Iron, Your Glade Plugins, Grandma's Life Support, etc.
Only things that should be turned on are your conditioner, interface, and computer. Light some candles so you can see, it'll be romantic. Use a wired mouse and keyboard. Disconnect your wireless mouse/keyboard sensor. Disable/disconnect your wiress NIC card. Turn off your cell phones.
If the noise still persists get the longest cable you can and take the guitar into another room. You can't use a shitty cable for this either though or you could induce other issues.
