Horn going off in middle of the night!

I awoke the other night to constant blare of a truck horn to realize it was from my 2005 Avalanche!

It was a solid blare and when I hit the key fob I could not turn it off at all.  I got in started it and it was still on, I then closed the door and it shut off.  Thinking it may be alarm related I manually locked all doors so alarm was not set.  30 minutes later it went off again.  This time I hit the key fob and still nothing, but it did turn off when I opened the door!

What could be causing this?  I have switched the relays but I don't think this is it, as that would not explain the behavior.  Also I don't believe a wire short would either, as the horn would stay on regardless of the door being open or closed, or alarm off etc.!

Open to ideas on how to test out a route cause!

Tks

Did you get a car wash recently?
I had that happen to me once not long after I came from the car wash. I could not figure out the root cause and I was heading out for a 1000 mile trip at the time. I simply pulled the horn relay out for a few days. After I got back I put the relay back in and it hasn't happened since. I think in my case it must have been some waterlogged connection somewhere

Nope, no car wash.  It had rained earlier in the day, but it went off in the middle of the night, a full 5-6 hrs after I drove it last. 

I've pulled the fuse for now as am reluctant to be awoken, and wake up the whole neighborhood, again in the night.  (Why do these things always happen in the middle of the night!)

Glad to hear though after it happened to you it hasn't happened again...but it makes me wonder what caused it!

Does the horn start sounding different after a few minutes, kinda like the battery may be dying?  I ask because that may be the issue.  I'm still unfamiliar enough with the Avalanche to even know if this is a possibility in this vehicle, but I've seen some weird stuff that can be caused by a battery in the process of giving up its ghost.  And I've read elsewhere on other vehicles to where the horn sounding off is an indicator of this. 

No, it sounded louder than ever in the middle of the night.  Battery indicator is showing it strong too, so I don't think its the battery.

Relay or Horn Switch or I think BCM sounds horn for alarm etc.

Good thing it's not a train horn. 

Usually when it goes off at night it is a temperature related problem.......this was a classic problem with GM's innovative rim blow steering wheel horns in the 60s......if pulling the horn relay stops it, it may be a problem with the horn contacts under one or both steering wheel "horn logos" or wiring in the steering shaft's clockspring winding mechanism shorting out as the temperature cools and metal contacts contract........slamming the door or hitting the steering wheel may temporarily disrupted the short. (The horn on their rim blow steering wheels would automatically silence as soon as the battery died or the steering wheel melted, whichever came first)

Here's some new information....
I put the fuse back in after a week or so and it was fine for a couple of weeks and then it went off again.  I took the fuse out but since then the cruise control is not working and I got a message to service the air bags, so I'm thinking this could be 'computer related' as any of the 'solid state' explanations don't seem to hold up to the symptoms.

But what computer controls these things...is it the ECM or is that just for the motor?  Any ideas on how I can confirm the diagnosis.  I will put the reader on this weekend to see if it can tell me anything...

Tks.

Did you put a new relay in it?

Yes, I swapped the one relay for a working one and it still isn't working.

I suspect it's something in the steering column that would explain why the cruise control is not working.

Do the horns work if you press the airbag on the steering wheel.