Hi, welcome to Just Answer.
There is a Chime Module under the left hand side of the dash...below the steering column. Commonly it fails causing the audible warning to cease working. Usually you can get to the module and tap it with the back of a screwdriver and it may begin temporarily working again, if so it further condemns the chime Module. It is correctly tested through a factory level scan tool...
Rip
Lead Technician
BMW Factory Training, ASE Master Techinician, Advanced engine performance.