Gang not allowed to be heard? (4)
I believe the answer is:
band
'gang' is the definition.
(I've seen this before)
'not allowed to be heard?' is the wordplay.
'not allowed' becomes 'banned'.
'to be heard?' indicates a 'sounds like' (homophone) clue.
'banned' sounds like 'BAND'.
(Other definitions for band that I've seen before include "See 23" , "Pop group, perhaps" , "Music ensemble" , "Outline drawing" , "Loop; rock group" .)