Warning from quartet that’s audible (4)
I believe the answer is:
fore
'warning' is the definition.
(shouted in golf)
'quartet that's audible' is the wordplay.
'quartet' becomes 'four' (synonyms).
'that's audible' shows a homophone (sound like).
'four' sounds like 'FORE'.
'from' acts as a link.
(Other definitions for fore that I've seen before include "Fairway warning" , "Warning cry on a golf course" , "Ancestor" , "The front part of a ship" , "Word of warning to golfers" .)