I had a 12kt and a 18kt "hum". I faired out the daggar and rudder trailing edges and removed the 12kt hum, but the 18kt hum remained. Over 18 kts, and the wind, water, and boat was making so much noise I couldn't tell if it faded out again or not....

Someone told me to fair the trailing edges unequally (like an airplane wing trailing edge) so that the edge does not vibrate as much as a symmetrical edge would.