St. Joseph Hospital of Orange - If You Snore You May Be Suffering From:

Poor muscle tone in the Tongue and Throat. When muscles are too relaxed, either from alcohol or from drugs that cause sleepiness, the tongue falls backwards into the airway or the throat muscles draw in from the sides into the airway. This can also happen in deep sleep.
Excessive bulkiness of Throat Tissue. Children with large tonsils and adenoids, for example, often snore. Overweight persons have bulky neck tissue, too. Cysts or tumors could also cause bulk, but they are rare.
Long Soft Palate and or Uvula. A long palate narrows the opening from the nose into the throat. As it dangles, it acts as a noisy flutter valve during relaxed breathing. A long uvula makes matters even worse.
Obstructed Nasal Airways. A stuffy or blocked nose requires extra effort to pull air through it. This creates an exaggerated vacuum in the throat, pulls together the floppy tissues of the throat, and snoring results. So, in some persons snoring might occur only during the hay fever season or with a cold or sinus infection.

Also, deformities of the nose and nasal septum, such as a deviation of the septum (a deformity of the wall that separates one nostril from the other), can cause an obstruction.