What may illuminate mild recall of unhappy sound? (9)
I believe the answer is:
lightbulb
'what may illuminate' is the definition.
I can't judge whether this definition defines the answer.
'mild recall of unhappy sound?' is the wordplay.
'mild' becomes 'light' (I've seen this before).
'recall of unhappy sound?' becomes 'bulb' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'light'+'bulb'='LIGHTBULB'
Can you help me to learn more?
(Other definitions for lightbulb that I've seen before include "Glower" , "such an illuminating thing!" .)