I'm a motorcyclist too, and straight piped Harleys make me stabby. I don't believe they're louder on the highway. I believe they're louder whenever they're within earshot of any place where people congregate without earplugs (cafes, restaurants, pedestrian areas), whereupon the scumbag on the seat finds it necessary to go wide-open throttle to show off how terrible their bike sounds. It never fails.
