Herald quietly agrees changes (7)
I believe the answer is:
presage
'herald' is the definition.
(I've seen this in another clue)
'quietly agrees changes' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'changes' indicates an anagram.
'agrees' with letters rearranged gives 'resage'.
'p'+'resage'='PRESAGE'
(Other definitions for presage that I've seen before include "Foretell" , "Portent" , "Forecast, foreshadow" , "Be a sign or warning of (an event)" , "Be a sign of (something)" .)