I've found many posts in the forums about issues on DPs where the parking brake alarm does not silence even after the air parking brake has been released. Mine was doing this. It would beep for awhile then stop, and maybe start up again for no apparent reason.
Others have commented their problem was a defective sensor on the switch. I finally got brave and pulled the panel off the driver side console to diagnose the issue. It quickly became obvious to me that the parking brake switch itself was loose. Tried to tighten, but one of the screws was stripped.
So it seems that all the downward pressure to release the parking brake caused the threads to strip and the switch became more and more loose. Turns out the machine screws go all the way through the flange on the switch so I just got some nuts to back them up and got the switch firmly seated.
SO glad to have this resolved. I just never noticed that the switch was loose - I don't tend to look at it when I am activating or releasing it.