All the in-ear earphones I've used with my Mi8 have this background "crackling" sound when I'm listening to audio. It's more obvious if the music is softer with fewer instruments in the background. For example, if the beginning of a song is instrumentless, then I can hear this krr-krr-krr sound, like very soft rattle-snake sound? At first I thought it had to do with the impedance of my earphones, but I've tried very high impedance earphones and still can hear the sound. My brother uses Mi8 and the problem is also present in his, so it's not something isolated. What to do?

I am guessing it doesn't have a headphone jack, and to use normal earphones we need to plug in the white colored interface. Perhaps that's the problem?