On duty (CCK) staff reported air hissingsound came from Rear DT. Staff (YWT) checked and confirmed, air discharged sound heard from outside train.TC feedback M R pressure at 10 bar. ~~~~~ Check and found #3501-A/S wheel flange air tubing (L) connector spoil, replace and function test ok. Done by Jack/Sateesh/Koh. 22/05/20.