Hmm...haven't heard that before, is it when the engine is running or just on accessory?
The car will bong when the door's open or if your seatbelt isn't fastened. It will do a loud fast paced ding for about 5 sec, then stop, then repeat until the seatbelt is fastened or the car is shut off. At least that's what it does in mine, but everything's digital on the 03's. Do you know if an aftermarket alarm system was installed within the car?
Sorry I can't be of more help. You may want to post it in the 4.6 section of the forum.