As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
COCKPIT/CABIN NOISE: CLIMBING ABOVE 38000 FT THE CABIN CLIMB RATE BEGAN TO SPIKE AND DESCEND BETWEEN PLUS/MINUS APPROXIMATELY 1800 FT PER MIN FOLLOWED BY A LOUD AIR NOISE ON THE COPILOT'S SIDE. WE DONNED THE MASKS AND DESCENDED AND RETURN TO OUR DEPARTURE AIRPORT.