Default [Q] Stop music playing when connecting to bluetooth

Hi,

Got a seriously annoying problem. Whenever my phone connects to bluetooth, which is usually in my car, it starts playing the last song I listened to by auto launching google play music and playing away. I don't know if I'm being blind but I can't find a setting to turn this off. Sometimes I might want to stream music in the car, but not automatically on connecting!

Any ideas?

Thanks!
Devices: Nexus 4, Nexus 5 & Nexus 7 (2013)