Music Player doesn't work well when screen turns off and locks

[AC Question]

Hi. Weird thing started a few days ago. When I play something in Music Player (same tracks as before), it works well first, but when i put down the phone and its screen dims, music player starts making funny noises and plays a bit slower, like it's facing memory issues. When i turn the screen back on, the problem disappears. It looks like something screws with my memory or CPU when the LCG goes off. Any idea??