You don't need to scrape (in case that wasn't quite clear from Daniels reply)...However; if you find a metalic object (e.g. a coin) and (providing it doesn't stick to your pick-ups...which is kinda annoyin') you can get so really cool, alien sounds...sorta like when UFO's are landed it makes me think of.....Nothing to do with tremolo picking....but you got the nail on the head...as many times for that beat then move on to the next...
Hope that helps