For 1990-2009 cars
A harsh tone: Caused by loose bolts in the sheet metal mounting area.
A low pitch moan: Caused by too high a current. Adjust the horn as necessary.
A weak tone: Caused by too low a current. Adjust the horn as necessary.
A weak strained tone: Caused by a foreign body in the horn that should be shaken out or removed.
A harsh vibration: Caused by the horn contacting the sheet metal. Bend the bracket in order to give the horn clearance and freedom from the interference.