A well known manufacturer makes them for Ford Racing and they have a characteristic sound. Slight hum compared to the original at 2000 rpm, which is a very common rpm for most rides. But after a few hours on the freeway, we didn't think about it, and it didn't kill the stereo. For example buffing on 4 inch tips. They protrude slightly from the bumper. Quiet when you want and moderately loud when you walk.