Nexus 5 - How come Google Play Music uses up so much battery?

[AC Question]

I have a Nexus 5, and whenever I listen to music with Google Play Music, it drains the battery like crazy. I have the phone in airplane mode, location, WiFi, and everything is off. I have screenshots that I can show you, but the phone went down about 35% in an hour with Google Play Music at the top of the usage list.

Also, the phone gets VERY warm when I listen to it for a little while.

Any help would be greatly appreciated.