Chorus starts to serenade in noisy group (4)
I believe the answer is:
sing
'chorus' is the definition.
(I've seen this before)
'starts to serenade in noisy group' is the wordplay.
'starts to' indicates taking the first letters.
The first letters of 'serenade in noisy group' is 'SING'.
(Other definitions for sing that I've seen before include "Inform - carol" , "Turn informer" , "serenade" , "Chorus" , "behave like noisy tits" .)