Factory alarm is the PATS system and a blinking light in the dash to just let those who look in your car know.
Sounds like an aftermarket alarm. Look under your dash for wiring and in the engine bay. Has to be a part that makes that noise and i would start tracing back the wiring from it. If you don't have the remote for it and the company is out of buisness, i would remove it from the car. go with another one from a reputable company. hope this helps.
oh, or take it to a shop that installs aftermarket alarms, they should be able to help alot better than Ford can.