2006 Sebring sedan's horn honking steadily when car is cold. Why???

When my car sits overnight in a parking lot and temps get into low 20's, when I start it up within a couple minutes the horn starts blowing.  I put pressure on the horn part of the airbag in the steering wheel to get it to stop.  When the car warms up, I can hit the wheel and it will stop.  Happened every time for the last month.  Help!  Took it to a mechanic who took the wheel cover off, disconnected the horn and reconnected it but it still happens.