Channel took off by the sound of it (4)
I believe the answer is:
flue
'channel' is the definition.
(flue is a kind of channel)
'took off by the sound of it' is the wordplay.
'took off' becomes 'flew' (I've seen this before).
'by the sound of it' shows a homophone (sound like).
'flew' is a homophone of 'FLUE'.
(Other definitions for flue that I've seen before include "Tube" , "Conduit for smoke" , "Vent pipe for smoke, etc" , "Chimney shaft" , "Small chimney" .)