As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LOUD SQUEALING DURING TAKEOFF AND CABIN PRESSURIZATION INDICATED 1500 TO 2000 FPM DOWN AND ABORTED TAKEOFF. TROUBLESHOOTING AND FURTHER ENGINE AND PRESSURIZATION RUNS COULD NOT DUPLICATE THE PROBLEM. BELIEVE TO HAVE BEEN A STICKY OUTFLOW VALVE DUE TO NOT FLYING IN FOR A LONG TIME.