Sometimes the heat from the engine is the cause for the problem. Past years bikes had the horn mounted behind the rear cylinder under the seat (FXDWG) and they had a relocator kit to mount it where they are now which cured the problem.
There's usually a small screw on the back of the horn that can be used to tweak the adjustment but don't move it too much and remember where it was to start. It will usually cure the problem of the "sick moose " syndrome.
