I had my small shop-vac sitting in the drivers side floor area while I was vacumming today when all of the sudden the horn started blowing non-stop. I turned off the vacum and grabbed the keys and started trying to turn off what I thought was the alarm on the truck. No luck. I put the key in the ignition, turned it to on, horn still blowing. I then started the truck. Nothing changed. The horn finally stoped. I turned the vacum back on, same thing. Horn going nuts. Moved the vacum to the rear compartment thinking that there might be some sort of glass breakage sensor installed from the factory that was being tripped by the noise of the vacum. No problem after that. I do not have any thing other than the factory equipment on my truck, no after mkt. alarm. Any ideas what might have been causing this?