Instrument, note, is one that plays itself (7)
I believe the answer is:
pianola
'instrument note is one that plays itself' is the definition.
'Pianola' can be an answer for 'instrument' (Pianola is an example). I'm not certain of the remainder of the definition.
'instrument note' is the wordplay.
'instrument' becomes 'piano' (piano is a kind of instrument**).
'note' becomes 'la' (I've seen this in other clues).
'piano'+'la'='PIANOLA'
Can you help me to learn more?
(Other definitions for pianola that I've seen before include "Mechanical keyboard instrument" , "A bridge hand easy to play" , "Automatic instrument" , "Melody Maker" , "Keyboard without a keyboarder!" .)