Horn came on?

My wife came in this morning and told me it sounded like the horn was on in the Alero. So I went to see and it was on , but not very loud. It was a constant sound not like an alarm. When I put the key in the ignition and turned it on it became loud like a horn should. When I turned it off it quit. Anyone else have this happen? Not real sure what to look for. Any help or comments appeciated. Thanks , Guitarz