Nico in play about mischief - it's not The Sound of Music? (10)

I believe the answer is:

inharmonic

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'not the sound of music?' is the definition.
I can't tell whether this defines the answer.

'nico in play about mischief' is the wordplay.
'play' indicates an anagram.
'about' means one lot of letters goes inside another.
'mischief' becomes 'harm' (I am not sure about this - if you are sure you should believe this answer much more).
'nico'+'in'='nicoin'
'nicoin' with letters rearranged gives 'inonic'.
'inonic' placed around 'harm' is 'INHARMONIC'.

'it's' acts as a link.

Can you help me to learn more?

(Another definition for inharmonic that I've seen is " Not nice to hear".)

I've seen this clue in the Irish Times.

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