Cut makes one grumble audibly (4)
I believe the answer is:
mown
'cut' is the definition.
('mown' can be a synonym of 'cut')
'one grumble audibly' is the wordplay.
'one grumble' becomes 'moan' (I've seen this before).
'audibly' shows a homophone (sound like).
'moan' sounds like 'MOWN'.
'makes' acts as a link.
(Other definitions for mown that I've seen before include "(Of grass) cut" , "Block of cast metal" , "Cut down with a blade" .)