Organ piece in which one note has to ring out! (5)
I believe the answer is:
pedal
'organ piece' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'one note has to ring out' is the wordplay.
'one note has' becomes 'd' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to ring' becomes 'peal' ('peal' can be a synonym of 'ring').
'out' indicates putting letters inside.
'd' placed inside 'peal' is 'PEDAL'.
'in which' is the link.
Can you help me to learn more?
(Other definitions for pedal that I've seen before include "work with press from Oxford?" , "Foot-lever" , "part of organ" , "ride a cycle" , "Brake or clutch perhaps" .)