Noisy electrical buzz when recording guitar

I'm getting back into recording now that I've got my fancy new Mac Mini and some audio equipment. I remember trying this a while back and once I started I realized I still had an issue which was bugging me last time I tried to do this - feedback "line noise", a deep electrical buzzing sound on the track. Bah!!!

It sounds gross and there are a few ways to get rid of it, it seems. The one is to add a Noise Gate filter to my GarageBand project (a Hi Pass Filter), filtering out the low frequencies. Problem there is I don't know exactly the frequency level of the buzz and I don't want to negatively affect the low guitar tones as they really fill out the sound. So that's not the best solution. Also, if you post-filter the noise like this, then if you want to play and have instant "monitor" feedback through earphones, you get the buzz while you're recording which is really distracting.

I realized pretty quickly that it's a grounding problem. If I put my hand on the guitar cable going from guitar to the mixer then the buzz goes away as I am grounding it. So I looked into some grounding methods and one suggests that you fiddle with how your computer is hooked up. I've heard that before as well, that you should make sure everything is on the same powerstrip/outlet to reduce electrical noise on the audio line. That didn't fix it and I tried a few combinations and plugged the mixer in separately to the wall outlet and still had the problem.

Next up I am going to probably buy one of these Radio Shack Ground Isolation (or Ground Loop) Filters. That is some sort of mini transformer that filters out the electrical noise from an audio line. We'll see if that works. I think they are only about $12 so I'll prob just try that out.

As I'm writing this I just realized there's another solution I haven't tried - just attach the guitar DIRECTLY to the Mac Mini's record input port, it's probably shielded and everything so I bet it would give a good signal. The negative of that is I don't get to connect to the nice soundboard and split the connection up into a stereo feed but I wonder if GarageBand can already handle that situation. I might try that too, and then just use the Sound board only for the Mic recording.

[Update: I tried connecting the Acoustic-Electric directly to the Mic input of the Mac Mini via a 1/4" to 1/8" mono connector, then selecting Mono input in GarageBand. Still no dice. I get the same grounding feedback problems as I did when going through the mixer, but without the benefits and ease of using the mixer. So this isn't a good solution either. I am gonna try getting a Ground Isolation filter and see if that solves the issue.]


[Update #2: I forgot I also have a USB interface called the Griffin iMic, you plug your audio input into there and then plug that into a USB input of the computer instead of using the Line In port on the computer. I figured this would be a sure-fire win... and... nope!!! Still get the grounding issue. I'm starting to wonder if maybe it's an issue with the pickup on my guitar or something. Anyway I'm prob gonna try the Ground Loop Isolation filter dealie first since they are like $15 or so and that'll be cheaper than taking my guitar in and less hassle than more fiddling with these wires. So we'll see if that works, I'm a bit surprised that the USB interface still picked up the grounding noise. Guess it's pretty intense!]