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!
Matt's work blog 
Dude thank you SO MUCH. I was convinced that I need to repair it. Who could have know that it is as simple as this! The thing is that mine worked with phones, but cracled when conected to aux. Thank you soo much!
You, sir, are a hero.
i pluged my iphone 6 to speakers and cracking sound came then at night i pluged headphones in it then again ssmehappening but headphone are alrite as i checked in other iphone they r working but not in mine how to fix that cracking sound plzz help me
Did you read my post? Try cleaning the headphone port on your iPhone. If that doesn’t work, go away.
Classy? Not.
This worked for me! Thanks
use a toothpick metal can damage the port
same symptom. flashlight and stick pin produced a huge piece of lint. no more crackling/shorting. thanks!