Discovering singular sign of discontent? (8)

I believe the answer is:

rumbling

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'discovering' is the definition.

'singular sign of discontent?' is the wordplay.
'singular' becomes 'rum' (synonyms).
'sign of discontent?' becomes 'bling' (I can't justify this - if you can you should give a lot more credence to this answer).
'rum'+'bling'='RUMBLING'

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(Another definition for rumbling that I've seen is " Continuous deep noise like distant thunder".)

I've seen this clue in The Independent.

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