What usually causes snoring when a person is sleeping?

Snoring. Snoring is just the sound of turbulent airflow passing through a slightly collapsed or crowded oropharynx or back of the throat. It is just a sound but it is a sound that makes us suspicious for potential underlying sleep apnea. Keep in mind that 65-75% of individuals that do snore have some level of underlying osa. Also, mild snoring can arise from chronic nasal congestion as well.
Narrowed Airway. Obstruction leads to snoring. The nose the back of the throat, tonsils, uvula and the back of the tongue can all lead to blockage which in turn leads to disturbed breathing and snoring.