I'm quiet - but he probably won't be (3)

I believe the answer is:

imp

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'he probably won't be' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

'i'm quiet' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'im'+'p'='IMP'

'but' is the link.

Can you help me to learn more?

(Other definitions for imp that I've seen before include "pickle" , "Emperor" , "Scamp" , "Little mischief-maker" , "puck" .)

I've seen this clue in The Globe and Mail.

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