Quietly consume some fuel (4)
I believe the answer is:
peat
'some fuel' is the definition.
(peat is a kind of fuel)
'quietly consume' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'consume' becomes 'eat' (eating is a kind of consuming).
'p'+'eat'='PEAT'
(Other definitions for peat that I've seen before include "Fuel from boggy land" , "Fuel from marsh" , "Dried turf" , "load of stuff in the garden?" , "Tape around turf" .)