I agree it could be sleep apnea (serious health condition) or another health condition such as allergies. Most people who snore need to see a doctor. In the meantime, try to have him sleep on his side rather then his back.
Some degree of sleep apnea is the likely culprit. You can always try gimmicks like 'breathe right' adhesive strips, and other strange solutions, but your best bet is to make him a doctors appointment to determine the best option. Or. . .as my Ma used to treat Da, plug his nose, lol. Not extremely effective, but infinitely entertaining!
I usually nudge my gf to roll over she stops , I put my hand under her pillow slightly moving her head she stops .. I tickle her lip .. And she stops snoring .. In extreme cases put a sock in her mouth !!! Jk!
Get him to a cardiologist for a full assessment - like an angiogram CT. There are other conditions that can cause this - such as a defective (possibly through injury) airway passage, obstructive sleep apnea, a problem with his jaw muscles when they relax (again possible through injury or even a congenital defect), etc. - try to get him to sleep on his side - the problem usually disappears as opposed to sleeping on his back. He can also wear a teeth guard to prevent his jaw from slipping back while sleeping - or a facial sling that is like an ace bandage that holds is mouth closed - but these are just quick fixes - you need him to see an MD (see a cardiologist as I mentioned, first) to get an assessment - he may need to take a few tests.