I'm with Eager on this one. My '79 and '83 both began dinging when I would take a sharp righthand turn. Finally determined that the switch in the door was not being fully depressed. This can either be the cause of a mal-adjusted switch, or the door itself being out of alignment. As a stop-gap fix, I taped a small piece of cardboard to the metal on the frame where the switch touches. Since my car's black, and I used electrical tape, you really can't even see it, so it's still there till the car goes in for full body overhaul.
Anyway, try opening the door and pushing in the switch, and see if that makes it stop..