Inapt, I'm playing percussion instrument (7)
I believe the answer is:
timpani
'percussion instrument' is the definition.
(I know that timpani is a type of percussion instrument)
'inapt i'm playing' is the wordplay.
'playing' is an anagram indicator.
'inapt'+'im'='inaptim'
'inaptim' with letters rearranged gives 'TIMPANI'.
(Other definitions for timpani that I've seen before include "Features of kitchen" , "Those beaten" , "set of instruments" , "orchestra members" , "Set of kettledrums" .)