Loud man's accidental stroke of luck (5)
I believe the answer is:
fluke
'accidental stroke of luck' is the definition.
(I've seen this in another clue)
'loud man's' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'man' becomes 'luke' ().
'f'+'luke'='FLUKE'
(Other definitions for fluke that I've seen before include "One lucky" , "part of whale" , "Lucky shot" , "flounder" , "Accidental stroke of good luck, or part of whale's tail" .)