Drop D Tuning. Minus the feedback, and the little intro (which may or may not be played on a keyboard, but could easily be picked up by ear on guitar) this is really all the guitar does during the song. E|---------------------------------| B|---------------------------------| G|-----------------------------5-5-| D|-1-1--1--1-1--1--5-5-5-5-3-3-5-5-| A|-1-1--1--1-1--1--5-5-5-5-3-3-3-3-| E|-1-1--1--1-1--1--5-5-5-5-3-3-----|