Note in sort of rock something sharp (5)
I believe the answer is:
prong
'something sharp' is the definition.
(I know this)
'note in sort of rock' is the wordplay.
'note' becomes 'n' (abbreviation).
'in' means one lot of letters goes inside another.
'sort of rock' becomes 'prog' (progressive rock is a music genre).
'n' going inside 'prog' is 'PRONG'.
(Other definitions for prong that I've seen before include "Something piercing" , "Fork part" , "tip?" , "Spike of fork etc" , "Point of a fork" .)