If you find that music on your iPhone crackles when you listen through your headphones, try cleaning the headphone jack.
Because your iPhone lives in your pocket, pocket lint can accumulate inside your iPhone’s headphone jack.
I had 3 years of accumulated pocket lint inside my headphone jack, without knowing about it. For months I thought the iPhone was dead and I’d need to replace the headphone jack which is very difficult.
The solution – just get a bent paperclip and scrape it all out. Voila! No more crackling music!