Noise always reveals criminal (9)
I believe the answer is:
racketeer
'criminal' is the definition.
(racketeer is a kind of criminal)
'noise always' is the wordplay.
'noise' becomes 'racket' (racketing is a kind of noising).
'always' becomes 'eer' (poetic way of saying ever).
'racket'+'eer'='RACKETEER'
'reveals' is the link.
(Other definitions for racketeer that I've seen before include "Crook" , "Mafia-type" , "Fraudulent dealer" , "who knows way round court, you might say?" , "someone to make a dodgy deal?" .)