Just had the same issue with my 99 F/L chassis, three days ago on the trip south.
Found that there are separate sensors for the alarm and the " park brake indicator light " . My buzzer was on and the light was not. No air leaks in the park brake release system. So I disconnected the buzzer for the rest of the trip and I'm looking for the sensor now that I'm parked for the winter.
My two sensors are mounted above the differential on the inside of the drivers side frame rail.
Sorry I can't post a picture of the location , as the coach is too close to the ground now that I'm in my winter site, and I forgot to take one while I was under checking for air leaks.