The "dive bomb" is a guitar technique in which the tremolo bar is used to make a noise considered to sound like a bomb being dropped. On of the most recognized pioneers of this technique is Jimi hendrix. Other notable musicians whom are widely known for using this technique are Eddie VanHalen and Dimebag Darrell.
One technique derived from the dive bomb is known as the "harmonic squeal", made famous by Dimebag Darrell of the heavy metal groups Pantera and Damage Plan.
One way to find the harmonic is to strike the string and lightly move your finger up or down the fretboard until the harmonic sounds. Then simply strike that note, depress the tramolo bar and lightly touch the string to sound the harmonic and then use the tremolo bar to manipulate the sound.