There are a few things that you can do to help fix the muffled sound on your LifeProof case. First, make sure that the case is fully charged. If it is not, it may need to be replaced. Additionally, make sure that the muffler is adjusted to the right level. If it is not, the muffler may need to be replaced. Finally, make sure that the case is closed completely when not in use. This will help to reduce the noise that is generated.