As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: ON DESCENT THROUGH 21,500 PRESSURIZATION PLUNGED TO 1200 FPM FOR2-3 SECONDS. THEN 700FPM 2-3 SECONDS THEN NORMAL RATE. PAX AND CREW FELT THE SURGE. FOUND DEBRIS STICKING OUT FROM OUTFLOW VALVE ( PIECES OF INSULATOR). OUTFLOW VALVE SEAL OK. NO DEFECT NOTED. ACCOMPLISHED OPS CHECK OF OUTFLOW VALVE IAW AMM 21-31-00.