Sound cycle: 'Hawk' (6)
I believe the answer is:
peddle
'hawk' is the definition.
('peddle' can be a synonym of 'hawk')
'sound cycle' is the wordplay.
'sound' indicates a 'sounds like' (homophone) clue.
'cycle' becomes 'pedal' ('pedal' can be a synonym of 'cycle').
'pedal' sounds like 'PEDDLE'.
(Other definitions for peddle that I've seen before include "traffic" , "Tout" , "Hawk, sell" , "Sell from door to door" , "sell my wares" .)