Pax feedback to staff (KTB) unusual sound heard at front M2 car. Staff (YCK) checked and confirmed b uzzing sound heard from the air-con. ~~~~~ 2522 Pax feedback to staff (KTB) unusual sound heard. Staff(YCK) confirmed buzzing sound heard from the air-con. CE checked 2522 humming noise from No.6 Line Flow Fan.  2522 L  #6 confirmed having humming noise. No spare available for c/o. Added to ADDL.  Helmi 44148 During 3wc check ok.No abnormalities found. Checked by Haffiz. 19/11/20