Horn blows intermittently with vehicle parked and off.

The horn on my 2010 Hyundai Elantra GLS goes off intermittently when parked and not running. It always blows 18 times, stops for about 5 seconds, then blows another 18 times. I can push the lock or unlock button on the key fob and it will stop, but will start again on it's own, for no obvious reasons. I changed the batteries in the key fob but that didn’t help. The TPMS light is also on solid, but I think that is a different problem as the light was not on when this issue started. I can pull the horn fuse and of course it will not go off. Any ideas would be appreciated.

Thanks!