As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RETURNED, EMER WAS DECLARED & LANDING WAS UNEVENTFUL. ACFT WAS OVERWEIGHT. DURING CRUISE AT FL 310 FLIGHT ATTENDANT REPORTED EXCESSIVE & ABNORMAL VIBRATION FROM ROW 24 REARWARD TO THE AFT OF THE ACFT. NO ENG INDICATIONS, VARIED POWER SETTINGS TO ISOLATE VIBRATION UNABLE TO VARY. FOUND NR 1 ENG INTERNAL BLEED DUCT CRACKED. R & R NR 1 ENG IAW MCM 71-91-99. OVERWEIGHT LANDING MCM 05-91-29 ACCOMPLISHED. SYS CHECKED NORMAL.