Staff (NEW) reported loud air dischargesound from rear DT car near the last 2 pair of doors. TC inf ormed there was no compressor fault and MR pressure was in t he healthy range. Staff (CTH) checked and confirmed loud dis ~~~~~ 3649 checked saloon interior for any abnormalities - OK. Checked U/F pneumatic system & found air dryer excessive air exhausting from exhaust port during change-over. 3649 air dryer & micro mesh filter replaced. Function test 2 min change-over & checked for air leak - OK. Performed pneumatic system check - OK (Checklist attached).  Lee PT/Shafie 08/11/2021. #3649 Air Dryer S/N : OLD : 3514/00/03 NEW : 0137-4348