This fun
technique was has been popularized by
Steve Vai,
Nuno Bettencourt, and
Joe Satriani.
Make sure to have your gain, or overdrive, up a bit. A Floyd Rose Tremelo is ideal, but any bar will work.
Rotate the whammy bar away from the neck. Play any note, and; starting at the base of the bar, apply pressure and slide your finger towards the end, and let your finger slide off the end. The bar should *pop* up, causing a gargle sound.