Instrument's power level is over quiet (6,5)
I believe the answer is:
player piano
'instrument's' is the definition.
(player piano is a kind of instrument)
'power level is over quiet' is the wordplay.
'power level' becomes 'player' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'is over' says to put letters next to each other (in a down clue, some letters go over others).
'quiet' becomes 'piano' (I've seen this before).
'player'+'piano'='PLAYER-PIANO'
Can you help me to learn more?
(Other definitions for player piano that I've seen before include "Automatic instrument" , "appearing in nickelodeon once" .)