Sound container in larynx (5,3)
I believe the answer is:
voice box
'larynx' is the definition.
('voice box' can be a synonym of 'larynx')
'sound container' is the wordplay.
'sound' becomes 'voice' (voice is a kind of sound**).
'container' becomes 'box' (box is a kind of container).
'voice'+'box'='VOICE-BOX'
'in' is the link.
(Other definitions for voice box that I've seen before include "Organ" , "The informal larynx" .)