Your machine has a 15 amp fuse labeled HORN in the underhood fuse block.
Don't believe that can be your problem, though.  See description below:

The vehicle horn system is activated under the following conditions:

The horn switch is depressed.

On vehicles equipped with content theft deterrent (UA6), the body control
module (BCM) may command the horns on. The BCM commands the horns on under
any of the following conditions:
When the content theft deterrent system detects a vehicle intrusion. For
further information refer to Content Theft Deterrent (CTD) Description and
Operation in Theft Deterrent.
When the panic button is depressed on the remote control door lock
transmitter. For further information refer to Keyless Entry System
Description and Operation in Keyless Entry.

When the keyless entry system is used to lock the vehicle, a horn chirp may
sound to notify the driver that the vehicle has been locked. The
notification feature may be enabled or disabled through personalization. For
further information refer to Keyless Entry System Description and Operation
in Keyless Entry.

BEEEEEEEEEEEEEEEEPPPPPPPP!!

One possibility is your horn button might be suffering from heat warp.
Or the plastic sleeve the wire passes through inside the column broke
allowing the end of the wire to touch the horn contact.

Good Luck

     Harryface    
05 Park Avenue, 32,648
91 Bonneville LE  304,555