Noisy breathing. Infants are often noisy with breathing. Untill they grow a longer neck, mouth breathing requires they arch their neck back. Most of their air passes thru rubery nostrils that vibrate with air movement & are susceptable to swelling from irritants, odors, dry heat etc. Tonsils & adenoids also contribute to airway narrowing. If you remove anything you can smell from babies air this should help.
Sleep apnea. Any snoring in an infant should be examined. It could be the result of allergies, or an obstructed airway due to enlarged tonsils and or adenoids, or a deviated septum. It can lead to sids or brain damage.
Allergic rhinitis. Most likely your baby has allergic rhinitis. This could be caused by formula, if you are formula feeding your baby or could be due to environmental factors. I see many babies who react to products like bounce that is used on the babies clothes, strong perfumes, colognes, cigarette smoke, etc. If you can eliminate all the environmental factors and you are breastfeeding, your baby should improve.