Brief success of Hannah's I felt bad keeping quiet (5,2,3,3)
I believe the answer is:
flash in the pan
'brief success' is the definition.
(I've seen this in another clue)
'hannah's i felt bad keeping quiet' is the wordplay.
'bad' indicates anagramming the letters.
'keeping' means one lot of letters goes inside another (some letters kept inside).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'hannahs'+'i'+'felt'='hannahsifelt'
'hannahsifelt' anagrammed gives 'flashinthean'.
'flashinthean' going around 'p' is 'FLASH IN THE PAN'.
'of' acts as a link.
(Other definitions for flash in the pan that I've seen before include "Nine days' wonder" , "First and only success" , "Brief success - flambe moment?" , "Brilliance that doesn't last" , "Ephemeral success" .)