Phantom Tunes

[Max Plankton]

I have an LG G3 which has a curious tendency to play music spontaneously (as well as take pictures of the inside of my pocket). I have a Circle Case, and assumed that when the case was closed the phone would effectively be in Sleep Mode. Then, while in a shop, music stated playing from my phone. This has happened a couple of times since, even after locking the phone with a PIN. Most people seem concerned about their phone stopping to play music without instruction, but I have the opposite problem and frankly it's beginning to get somewhat irritating. Any ideas?