One may hear quiet constituent (5)
I believe the answer is:
piece
'constituent' is the definition.
(I've seen this before)
'one may hear quiet' is the wordplay.
'one may hear' shows a homophone (sound like) (I've seen 'might hear' mean this).
'quiet' becomes 'peace' (I've seen this before).
'peace' is a homophone of 'PIECE'.
(Other definitions for piece that I've seen before include "Chessman - part - firearm" , "Firearm -- collector's item" , "king or queen?" , "newspaper article" , "Section; firearm" .)