I recently bought a Huawei Ascend Y520. I've noticed that when playing music through it, there is a fairly consistent low static/crackly noise through my Bluetooth headphones. This appears to be the case for music downloaded via Google Play Music, streamed through Google Play Music, YouTube and Pandora (though it's possibly a bit worse for the streamed music). It's not so bad as to make it un-listenable, but it is unpleasant seeing as that is one of the primary functions of the phone for me.

I think it is a Bluetooth issue, as the sound through the phone's speaker sounds fine, and the crackling doesn't appear when I use the headphones on another phone. The phone has Android 4.4.2 (KitKat), while the other phones I've tried it on have earlier Android versions. When Googling the issue, it seems like quite a few other people have had issues with KitKat and Bluetooth. However, it seems that most issues have been with the connecting not working or dropping out, which isn't the case for me (although it does sometimes seem a little choppy, I'm not sure whether that is Bluetooth or Wifi causing it).

I've tried unpairing and reconnecting and restarting the phone a few times, but that hasn't helped. I even looked into Developer Options to look at "Bluetooth HCI packets" as I saw recommended, but that didn't do anything either.