What was found
ABNORMAL NOISE, VIBRATION IN CENTER MAIN CABIN CEILING. CREW COMMENTS: OVERHEAD AIR NOISE LOUD BETWEEN ROWS 11 - 21 MAINT TEXT: OVERHEAD DISTRIBUTION PANELS OPENED AND CHECKED FOR LEAKS. NONE FOUND. AIRFLOW AT FWD CABIN CHECKS GOOD BUT BEGIN TO DIMINISH SIGNIFICANTLY TOWARDS AFT SECTION FROM ROWS 20 TO AFT. NOISE APPEARS A LITTLE LOUDER THAN NORMAL BUT NEEDS UPGRADE AND NOISE REDUCED. POSSIBLY NEEDS TO REVISIT CLEANING OF DUCTS, CHECK BAFFLES AND RESTRICTOR PLATES. OKAY TO CONTINUE.