Is bursting into it so useless? (4)

I believe the answer is:

song

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'is bursting into it' is the definition.
I can't judge whether this definition defines the answer.

'so useless?' is the wordplay.
'useless?' becomes 'ng' (I can't justify this - if you can you should believe this answer much more).
'so'+'ng'='SONG'

Can you help me to learn more?

(Other definitions for song that I've seen before include "Ballad, aria" , "Ditty" , "Vocal item" , "Vocal number" , "Lied" .)

I've seen this clue in the Evening Standard.

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