The background music and sound effects will stop playing, after completing a mission. The only sound effect I can hear is the blood sucking sound effects, and the sound of an item drop, but nothing more. They only way to fix this issue is to uninstall the game, and download it again.

I usually have to reinstall it 2 or 3 times a day, but even sometimes, after reinstalling it there'll be no sound, and i'll have to reinstall it again.