Try spraying some electrical contact cleaner in the female receiving end of the seatbelt buckle and inserting/removing the seatbelt latching tongue several times. If that does not work, you can temporarily disable the buzzer from sounding without shutting off the SRS airbags by following the steps below.
The Enhanced Warning System (BeltAlert) can be enabled
or disabled by your authorized dealer or by
following these steps:
NOTE: The following steps must occur within the first
60 seconds of the ignition switch being turned to the ON
or START position. DaimlerChrysler does not recommend
deactivating the Enhanced Warning System
(BeltAlert).
1. With all doors closed and the ignition switch in any
position except On or Start, buckle the driver's seat belt.
2. Turn the ignition switch to the ON position and wait
for the Seat Belt Warning Light to turn off.
3. Within 60 seconds of turning the ignition switch to the
ON position, unbuckle and then re-buckle the driver's
seat belt at least three times within 10 seconds, ending
with the seat belt buckled.
NOTE: Watch for the Seat Belt Warning Light to turn on
while unbuckling and off while re-buckling the seat belt.
It may be necessary to retract the seat belt.
4. Turn the ignition switch to the LOCK position. A
single chime will sound to signify that you have successfully
completed the programming.
The Enhanced Warning System (BeltAlert) can be reactivated
by repeating this procedure.
NOTE: Although the Enhanced Warning System
(BeltAlert) has been deactivated, the Seat Belt Warning
Light will continue to illuminate while the driver's seat
belt remains unbuckled.