Such a vocal piece is mayhem (5)
I believe the answer is:
havoc
'is mayhem' is the definition.
(I've seen this before)
'such a vocal piece' is the wordplay.
'piece' indicates the answer is hidden within the clue.
'HAVOC' is hidden within 'such a vocal'.
(Other definitions for havoc that I've seen before include "Widespread destruction and great disorder" , "Pandemonium" , "Chaos and destruction" , "Total destruction" , "Carnage" .)