from The Guitar F/X Cookbook
1) Electric guitar with a floating tremolo bar that can be pulled up (or back) pretty far
2) A lot of distortion
3) Reverb

This trick will make your guitar sound like an angry elephant about to stampede. Set your amp or distortion box to give you maximum distortion and add some reverb. Set your guitar’s pickup selector to the bridge position and turn the volume knob completely off. Now play Fig. 1 by hitting harmonics on the 5th fret of the G string, 7th fret of the B string, and the 12th fret of the high E string. Let all three notes ring together. With your right hand, turn your volume up quickly as you pull up on the tremolo bar with your left hand (below).

Download Example Audio

Make sure you have tons of distortion and all the harmonics are ringing clearly. Also, be sure you don’t accidentally muffle any strings when you reach down to turn up the volume knob.