Initially, this is common with the use of PAP therapy but typically resolves itself in time.  If you have issues with your stomach valve, pressure from your PAP therapy equipment may push air into the stomach. It is best to speak with your physician regarding this matter. Another cause is mouth breathing with a nasal mask leading to the swallowing of air. Clients may opt to try and train themselves in keeping their mouths closed during the night. A chin strap in conjunction with a nasal mask or the use of a full-face mask may help alleviate this problem.