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Part
of
gut
grumbling
softly,
upset,
having
received
nothing
(7)
Part of gut grumbling softly, upset, having received nothing (7)
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The definition is at the beginning of the clue.
How the clue works
Part of gut is the definition. Start with P for "softly" (the musical marking), then take SURLY meaning "grumbling", put it around O for "nothing", and reverse the lot ("upset") to PYLORUS.