Containers for a musical instrument, so we hear (5)
I believe the answer is:
sacks
'containers' is the definition.
(sack is a kind of container)
'musical instrument so we hear' is the wordplay.
'musical instrument' becomes 'sax' (sax is a kind of musical instrument).
'so we hear' shows a homophone (sound like).
'sax' is a homophone of 'SACKS'.
'for a' acts as a link.
(Other definitions for sacks that I've seen before include "Fires; large bags" , "Dismisses; bags" , "Gets rid of" , "sends up in flames" , "Plunders; fires" .)