Scientist's note found in box (7)
I believe the answer is:
chemist
'scientist's' is the definition.
(chemist is a kind of scientist)
'note found in box' is the wordplay.
'note' becomes 'mi' (as in 'do re mi').
'found in' is an insertion indicator.
'box' becomes 'chest' (chest is a kind of box).
'mi' going inside 'chest' is 'CHEMIST'.
(Other definitions for chemist that I've seen before include "Faraday, for example" , "Drug store" , "Shop selling medicines" , "Scientist; type of shop" , "Shop for drugs" .)