Quiet-sounding musical composition (5)
I believe the answer is:
piece
'musical composition' is the definition.
('piece' can be a synonym of 'musical composition')
'quiet-sounding' is the wordplay.
'quiet' becomes 'peace' (I've seen this before).
'sounding' indicates a 'sounds like' (homophone) clue.
'peace' sounds like 'PIECE'.
(Other definitions for piece that I've seen before include "Portion, coin, item" , "A part of something" , "King, perhaps" , "Bishop, for one" , "artefact" .)