can be because of chronic nasal congestion
deviated nasal septum, sleep deprivation (not getting enough sleep can lead to further throat relaxation), sleep position (snoring is typically most frequent and loudest when sleeping on the back as gravity's effect on the throat narrows the airway
or your mouth anatomy (having a low, thick soft palate can narrow your airway), alcohol consumption. Treatment depends upon cause. Losing weight, avoiding alcohol close to bedtime, treating nasal congestion, avoiding sleep deprivation, avoiding sleeping on your back
homeopathic treatment has very encouraging results. Consult online for details.