2007 Edge - horn honking after battery replacement

[bunnykins]

Hi there! I replaced the battery in my 2007 edge and now if I park my car and lock my doors after about a minute the horn honks once and continues a single honk about every 30 seconds. If I leave it unlocked there's no honking. I have an anti-theft system, it was already on the car when I bought it from the dealer (car was apparently a demo, had 5K miles on it), not sure if the alarm factory or after-market. The mechanic tells me I need to have the ford dealer re-flash or re-program the system (I think that's what he said). However I've talked to the service department a few times and they say they doubt it's related to the anti-theft system but if I bring it in and they hook it up to their diagnostic machine they can maybe find out. This didn't happen before the battery was replaced and it's driving me nuts. Any suggestions as to what I can try doing myself to try and remedy? I don't want to have to pay $$$ to the dealer if possible. Thanks in advance!