As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) WHILE IN CRUISE FLIGHT AT FL230 THE FLIGHT CREW OBSERVED THE PNEUMATIC PRESSURE GUAGE RAPIDLY FLUCTUATING BETWEEN 18 AND 23 PSI. THERE WAS AN ASSOCIATED CHATTERING HEARD IN THE AIRFRAME, IN CONJUNCTION WITH THE FLUCTUATING INDICATOR. FLIGHT CREW DECIDED TO RETURN TO BASE AND PNEUMATIC INDICATIONS RETURNED TO NORMAL DESCENDING THROUGH 15,000 FEET AND REMAINED THAT WAY TO LANDING. MAINTENANCE REPLACED PNEUMATIC PRESSURE VALVE/REGULATOR PN 101-380027-3 (PN 1H75-12). (TC NR 20071116002)