an anyone help???

Normally if I hit the steering wheel then the horn goes off!!! However, it seems to have developed a mind of its own over the last couple of weeks and likes sounding off whenever I hit the rear wiper and the indicator switch hmmmm,

I was driving through Guildford Centre earlier, went to indicate right and the horn went off next to a bunch of girls...

Needless to say they all started waving and smiling but I would prefer to have control over my horn...
Any idea's
