Sound of a step (5)
I believe the answer is:
tread
'sound of a step' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tread that I've seen before include "Step (heavily)" , "Surface of car tyre" , "A measurement of tyre" , "Staircase component" , "Top surface of a stair step" .)