As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING INITIAL DESCENT FROM CRUISE AS THE CABIN PRESSURIZATION CONTROL WAS SET TO A LOWER ALTITUDE THERE WAS AN IMMEDIATE & UNCONTROLLED RATE INCREASE OF THE CABIN VSI & CABIN ALTITUDE FOLLOWED SHORTLY BY A CABIN ALTITUDE ANNUNCIATOR & HORN.