I had the same fliggin problem with my p-10. Try to hit on some girl while your car is dinging away. The plug to my seatbelt was unplugged but the car would still ding. The dealers see it as a green flag to rip you off. The best advise I can give you is too get the courage up take out your gauge cluster and unplug the light for the seatbelt as well as the dinger (it is the silver box on the back of the cluster). I did this just recently while changing the color of my dash lights. It is so refreshing not to be asked "what is that noise", a thousand times a day. Hope this helps.
P.S. You may not consider this a valid option untill you get a estimate from the dealer.