Bought a 2004 ford suv. It's in nice shape.there's a slight beep that happens often. I have look thru the book and i go around checking?

Bought a 2004 ford suv. It's in nice shape.there's a slight beep that happens often. I have look thru the book and i go around checking?

The doors because the door ajar light comes on. At times it happens several times when i'm driving. Anybody have any idea why it keeps beeping, but not all the time, or is it a vehicle with character?