Sibling notes discomfort (6)
I believe the answer is:
twinge
'discomfort' is the definition.
(thesaurus)
'sibling notes' is the wordplay.
'sibling' becomes 'twin' (twin is a kind of sibling).
'notes' becomes 'ge' ().
'twin'+'ge'='TWINGE'
(Other definitions for twinge that I've seen before include "Emotional pang" , "A slight jab of pain (6)" , "Spasm" , "Sudden stinging pain" , "Sharp pang" .)