a) Ensure volume is set to maximum through Mobile Phone itself

b) Use suitable size of eartips and wingtips (can find different size of eartips and wingtips in accessories box)

c) Use other music APP/music player as different songs/videos app have different audio quality with different Mobile Phones 

(Different music APP customer can download from APP Store)

d) Ensure cleaning of eartips and validate this by image and ask customer to clean it carefully ( Do not use any sharp object to clean ear tips)