there might be several causes...
mine was the horn button at steering wheel jammed... or lost contact. So, press, sometimes at right angle, got horn, but most of the time tarak. So, i removed it and did some fixing.. done.
another prob i encountered was short circuit.. i sent to wireman to settle it for me. Sometimes it would just continue blaring the horn til i had to unplug the fuse. hahaha.. i still remember, that time it was 1am in the morning.. just got home... so as i opened the gate, i heard a soft beep of horn.. then i turned around.. eh.. no one but me.. kenot be wot... hantu meh? so nvm.. i fast fast parked the car in... go into my room.
then momentz later.. i heard horn blaring... and itz familiar.. crapz.. i went out.. kanneh.. itz my car. Straight i went to it and unplugged the fuse.. woke up the whole neighbourhood.. phaiseh phaiseh.
then another incident b4 fixing the horn, i was at the toll, 2nd car before my turn, an accord sorta look quite long to pay the toll charges, and my car suddenly decided to get impatient and horned by itself.. whoalau.. i damn malu wei.. the accord fella turned around and look at me... shit.. i scrambled to unplug the fuse again... even the toll booth attendent gave me a cruel stare. aiiii..........
wireman said some wiring prob la..dunno.. he just fixed it for me.. 10 buckz.. done.