Silly noise inside is really cruel (8)

I believe the answer is:

inhumane

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'really cruel' is the definition.
'inhumane' can be an answer for 'cruel' (similar in meaning). I am unsure of the 'really' bit.

'silly noise inside' is the wordplay.
'silly' becomes 'inane' (I've seen this before).
'noise' becomes 'hum' (humming is a kind of noising).
'inside' means one lot of letters goes inside another.
'inane' going around 'hum' is 'INHUMANE'.

'is' acts as a link.

Can you help me to learn more?

(Other definitions for inhumane that I've seen before include "Heartless" , "Callous" , "Not compassionate" , "Cruel" .)

I've seen this clue in The Irish Times.

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