As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BOI FLIGHT NR 2391 - LOUD BUZZING SOUND COMING FROM THE CABIN. BUZZING STOPPED WHEN POWER TRANSFER UNIT WAS TURNED OFF. MAINTENANCE REMOVED AND REPLACED PTU IAW AMM 29-11-61, PG 401-407, 501-503. BLED AND SERVICED NR 1 AND NR 2 HYD SYSTEM. GROUND CHECKS GOOD. AIRCRAFT RETURNED TO SERVICE