IPhone music volume changing?

Now I understand listening to a song at normal volume then the next song is a bit quieter, but what's happening is I'll listen to a song and then the next song will be blasting. I have to lower the volume by 2-3 levels. I know it's not my earphones cause I don't have volume control on them. Does anybody know why it does this?

That just happened to me, on my Kindle Fire. It could be the jack.
I know you can replace them. It is more likely that it there's a problem with the audio file itself, or the sound engine could be glitching.
Try turning your phone off and back on, or try a different song.

Try this: Go to settings, press "music" and turn on sound check.