game crashes when a strange sound comes

a sound of a zombie pig comes out of nowhere, like a cry of him dying the game crashes and then a message says: Minecraft pocket edition has stopped working and the game closes. every time he passed the field I heard the sound is the same, the bug only resolved when it is off the difficulty. ( It is not a duplicate !!! this error is strange is to be analyzed and corrected, there is because we are in 0.15.6 and all previous versions bugs still ??)