I believe that the Integated Control Unit (ICU) controls the warning chimes and control other things such as: intermediate wipers, rear window defogger timer, signal lights, oil warning light and a few other functions.
my money is on the door sensor. sometimes it works for me, sometimes it doesnt.
the sensor is a lil "L" shaped piece of plastic that when the door closes, it pushes that piece in, telling the car that the door is closed. now sometimes that signal stays open or closed. might wanna check that out