Greyed out songs when I plug my phone in (not sync)

Ok, so I've had this problem with each of my iPhones; 4, 5s, 6plus, where greyed out songs will get added to the phone after I plug it into my MacBook Pro.

It can't be the syncing, because I don't allow anything to sync with my phone except my contacts. I add/remove all of my music manually. So why are greyed out songs adding themselves to my iPhone every time I plug it into the computer? They are always duplicate songs of music that is already on the phone. I can delete them, but they just show up again when I plug the phone in, and the amount of greyed out songs that shows up is completely random.

I've tried having my phone sync with a playlist, but that takes forever, and didn't solve the problem so I went back to manual. Please help me fix this.