Request quiet, wanting heavy metal curtailed (4)
I believe the answer is:
plea
'request' is the definition.
(plea is a kind of request)
'quiet wanting heavy metal curtailed' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'wanting' is a charade indicator (letters next to each other).
'heavy metal' becomes 'lead' (I've seen this before).
'curtailed' means to remove the last letter.
'lead' with its final letter removed is 'lea'.
'p'+'lea'='PLEA'
(Other definitions for plea that I've seen before include "Appeal - with bargaining?" , "Request for mercy?" , "Formal statement of guilty or not guilty" , "(and 14) Enjoyment - gratification" , "Leap (anag.)" .)