Complaint as loud buzzer starts (4)
I believe the answer is:
beef
'complaint' is the definition.
(beef can mean a complaint or objection)
'loud buzzer starts' is the wordplay.
'loud' becomes 'f' (short for forte - 'loud' in music).
'buzzer' becomes 'bee' (insect which buzzes).
'starts' means one lot of letters go next to another.
'f' after 'bee' is 'BEEF'.
'as' is the link.
(Other definitions for beef that I've seen before include "Brawn; complaint" , "Grumble over cattle meat?" , "Meat - complaint" , "joint, perhaps" , "Brawn; grumble" .)