Originally Posted by: Dr_simonAre you using single coil pickups ?
Do you have fluorescent tube lighting near the guitar ?
Is your computer monitor on when you are playing ?
Have you eliminated any ground loops ?
Are there any other things that could be generating "electronic" noise in the vicinity.

All of these things are easily fixed and if not, then we can have another think.

Hey Dr! Thanks a lot for your help. My pickups are humbuckers (seymour duncan, jeff beck and jazz model), so I don't think that's it. No fluorescent lighting, but the TV is about 4 feet from me when I play (less than 2 ft from the preamp). Could that be it? I can't remember if it was on or off when I was playing so I'll try again. My monitor is a LCD monitor, so I don't think it can be a problem. My Korg preamp is on the computer and next to the TV, should I move it?

Also, the wire connecting the preamp to the computer is quite long and is "hi-fi" type, with a big jack going into female RCAs, then male RCAs going to a small jack... it's not a regular guitar jack.

How can I make sure that all my guitar metal components are properly grounded?

I'm going to try looking into all this things. Thanks a lot!