Pax feedback to staff(QUE) of cracking sound from RDT car undercarriage. Staff(DVR) checked & feedba ck that it was an air discharge sound from RDT car ~~~~~ 3536 Pax feedback to staff(QUE) of cracking sound from RDT car undercarriage. Staff(DVR) checked & feedback that it was an air discharge sound from RDT car  #CHECK & FOUND 'WFL' TUBE BROKEN. REPACED WITH NEW TUBE & ELBOW. FUNCTION CHECK OK.JIMMY,13/01/2020