electrical issue maybe?
 

I've got an 06 dually and for some reason about half the time when i back up the horn starts honking intermittently like the panic button was hit. it only does it in reverse but it's not all the time. has anybody ever heard of this. It's annoying as all hell.

im gonna guess that it only happens when your door is open??

its some kind of "safety feature"

Yep, door open and in rev will make the horn honk and lights flash. It was a safety "recall" on the truck...

same thing my truck does its a safety feature and it sucks.:argh: