While we breathe, either through our mouth or nose, air flows in steadily into our lungs. There relatively little to no sounds occurring when we are sitting and breathing quietly. While exercising, we produce more sounds since we breathe more quickly and the air likewise moves faster.
This is because while we move, our mouth inhales and exhales more rapidly, resulting in more turbulence to the airflow and more vibration to the tissues in our mouth and/or nose.
While we’re asleep, the area at the back of our throat oftentimes narrows down by relaxing and may even temporarily close. Since breathing remains constant, the airflow forces itself through a much smaller opening which causes the surrounding tissues to vibrate and create noise. Different people differ from reason to reason as to why they narrow down. The narrowing can be in the nose, throat, or mouth. Palatal snoring is such a case where snoring worsens because of nasal or mouth obstructions.