Protest: gather it is audible? (6)
I believe the answer is:
picket
'protest' is the definition.
(an industrial strike might include a picket)
'gather it is audible?' is the wordplay.
'gather' becomes 'pick' (picking is a kind of gathering).
'it is audible?' becomes 'et' (I can't explain this - if you can you should give a lot more credence to this answer).
'pick'+'et'='PICKET'
(Other definitions for picket that I've seen before include "Trade union protestor(s) outside a place of work" , "Group outside workplace encouraging strike action" , "Protest outside place of work" , "Wooden fencing stake" , "Strikers' blockade" .)