Nowadays, we find noise fading away in artists' recordings. Everything seems to be perfectly mastered and completely "censored" almost, removing those brilliant guitar noises that some of us cannot live without. Looking beyond the mainstream, there is still quite a bit of noise talent left, but i didnt come here to preach artists to try, I want to show you how to do it. So I'll start actually making my point. Unless otherwise stated, all techniques require high distortion.
I. Mid/High Feedback
Ah feedback, one of the simplest and most pleasureable techniques to get out of your guitar. To start, feedback generally requires two things: large amounts of distortion, and large amounts of volume. Volume is key here, unless you turn that amp up quite a bit, its going to be extremely difficult to get the desired effect, so crank that practice amp, screw the neighbors. You should get a squealish sound almost immidietly, to enhance the sound, point the back of the guitar at the amp, facing the pickups the opposite direction. This will make feedback even easier. Now this effect is all well and good, but to truly show brilliance, one can use what I would call harmonic feedback. This is manipulating your guitar to get a certain pitch that harmonizes the note youre playing. For example, get feedback while holding your finger on the third fret. Its likely that you got a tone that is either an octave, fifth, or third above the "g" (depends on what tuning youre in). You can control this by actually moving the guitar so that it faces the amp at different angles and distances, giving you different pitches and colors. Its not something easy to explain, you simply have to try it. Go crazy, squirm around, do the worm, dance, you should be able to find on your own various colors that you like. Try different hand positions, fret chords in addition to single notes. Go all over the fretboard.
II. Low Feedback
Also referred to as "drone", used by artists such as Sunn 0))) and Earth, this one is a bit more fickle. Do everything youve been doing for high feedback, except with the following adjustments:
01. Switch to your neck pickup.
02. Crank the "low" on your amp and/or pedal.
03. Strike the bottom string.
This tone is harder to sustain on its own, but gives a very heavy/doom quality to the sound.
III. Barring The Springs
While I don't believe this option is not available on all guitars, I'm positive it works with most tremelo equipped models. First, unscrew that backplate on your guitar. You should see two shiny, tempting springs. Now, apply much distortion, and play around with those springs. Scrape them with your pick, actually pick them, poke them, lick them, whatever, you should get a very unique sound coming from that guitar of yours. Again, experiment, see what different tones you can get. Van Halen liked this one.
IV. Playing Behind The Nut
Guitarist John5 occasionaly utilizes melodic behind the nut playing, as some of you Guitar World fans might have seen in the most recent issue. I'm simply going to tell you that these seemingly useless string bits are excellent noisemakers. Play around with them.
V. Broken Strings
So you're sitting there shredding, and you just broke one of your low strings. *Tear*. Now you have to go replace it and...wait. Stop. Noisemaking opportunity. Assuming that it's still attached, take that string and hit it with your palm right next to your pickup closest to the bridge so that it hits one of the pole pieces. You should get a squeal in addition to a low throbbing noise, that sounds very cool with some beatboxing prowness. Rythm (I know I didn't spell that right) is key to make this brilliant.
VI. Tapping On The Body Of The Guitar
Kurt Cobain liked to do this I believe. This is an excellent way to enhance high/mid feedback (Section I). It, like most everything in this article, is as simple as its sound. Hit your guitar. I'm serious, hit that thing. Try rapping with the knuckle and slamming with the palm, hit on the body for lower tones, hit the neck and headstock for mid/high tones. Experiment, see what you can do. The sound should vary for different guitars.
If these arent working for you, there are a few possible issues:
Turn up the volume and gain. Can't stress it enough.
Your guitar/amp may be designed to resist feedback.
If you have a noise gate, for gosh sakes turn it off.
Move close to the amp for feedback.
If these don't help, then my advice is crap.
Keep in mind that these are only guidlines, and not all techniques have been mentioned. forge your own methods in the hopefully growing realm of experimental guitar.