Ghetto? Quietly decline (5)
I believe the answer is:
slump
'decline' is the definition.
(I know that decline can be written as slump)
'ghetto? quietly' is the wordplay.
'ghetto?' becomes 'slum' (I've seen this in another clue).
'quietly' becomes 'p' (p for piano and quiet).
'slum'+'p'='SLUMP'
(Other definitions for slump that I've seen before include "Commercial decline" , "Sudden decline" , "Heavy fall" , "Bad economic recession" , "Sit badly" .)