Grumble when buzzer's loud (4)
I believe the answer is:
beef
'grumble' is the definition.
(thesaurus)
'buzzer's loud' is the wordplay.
'buzzer' becomes 'bee' (I've seen this before).
'loud' becomes 'f' (A musical term).
'bee'+'f'='BEEF'
'when' is the link.
(Other definitions for beef that I've seen before include "joint, perhaps" , "See 24" , "Bovine flesh" , "Muscle; meat; grievance" , "Complain; meat" .)