Muffled sound

When I play Clash Royale, Clash of Clans or Piano Tiles, the sound gets muffled after a few seconds. It starts out fine with clear sound and and volume but suddenly, the quality drops. The experience is similar to that of the music player lowering the volume when a message notification tone goes off.
Anyone experiencing this? How to solve?

from xda-developers http://ift.tt/2d98rpU
via IFTTT