Doesn't do it for all my music. Probably 70% of my tracks

If the common lead of the cord was open (broken), all you'd hear would be the difference between the left and right channels, which would cancel out stuff that was mixed to the centre, like vocals.

Can't be the files. When I use regular earbuds the songs play fine.
I think the Beats are fakes. There's no Micro USB port.

Where did you get the sound files? From a karaoke bar? It appears that something is removing the vocals on purpose. Since vocal tracks can't be eliminated completely, you'd hear some residual vocals, just like you describe. Since you've tried different players, it must be the files themselves. I don't know how the cans fit into the equation, if at all.

Tried my phone (galaxy note 5), iPod (old and hasn't been updated), and girlfriends phone too.

What are you using to play them? iPod, or a computer? Have you tried copying them to a different device and seeing if they sound different, or using a different set of headphones? I only ask these questiosn because it may be a hardware issue or software settings - iTunes for example has EQ settings in which you can adjust the sound of the audio.