Horn doesn't work with the ignition on

I own a 1996 Chevrolet Cavallier. The horn works fine with the ignition off; but after running the car for a short while, the horn area gets very stiff; and even pounding on that area won't sound the horn. Could it be an air-bag problem, where there is a slight inflation in the horn area? Where is the air-bag module located?

remove the airbag and see. dont turn the ignition on with the airbag disconnected otherwise a dealer will have to turn the airbag light off.