High pitch noise

Hey, I've been utilizing this site for a long time and have always found what I've needed. So thanks to y'all for that. Now I have an issue that I can't seem to get an answer to. This evening on the way home from work some roads were closed due to flooding. So I detoured several times and then I came to another road closed and with my brilliant self, I thought I would see exactly how bad it could be. Long story short, it got above my head lights so I back out. Truck seems to run normal, but the horn started blowing out of nowhere. Stopped and it quit. But now there's a high pitched continuous beep sound under the hood. Turn truck off and it continues. Have to disconnect the battery to make it stop. Any ideas? Thanks