Horn on 2000 C280

Before I call the dealer again can someone help!
While my wife is driving our C280 the horn will go off for no reason. She says it will happen at anytime. Today it was 2 times but the previous rash of occurences was a couple of months ago. She beats on the horn pad and it will eventually stop.
Could this be connected to anti-theft system?

I can't make the horn pad stick no matter what I do. I have been unable to duplicate and the dealer couldn't last time it was in.

HELP!