Thanks guys! That always puzzled me! I recently started an STP tribute band and I've been pushing to add "Coma" to our set list but we just couldn't figure out how they did it. The guitar player and I watched Rolling Rock 2.0 over and over and we noticed that there were shots of Dean doing something while that noise was heard, so we figured it was some kind of guitar effect but we were totally stumped as to how or what. I told him at one point that if it was me, I'd have that noise as a sample on some kind of sampler. My drummer doesn't have any triggers but I could probably pull it off by making a sample of that part and loading it to a Boss Loop Station.