When you swallow air, this can happen. It tends to go away after a while. (Couple of months) Some take meds for it, Gas-X is mentioned on the American forums. Others prop up the head-end of their bed so excess air comes out at the top, not the bottom.
Perhaps the pressure could come down on your machine or you may benefit form an Auto machine which doesn't sit at a fixed high pressure all the time. One other person had it disappear when using a humidifier but couldn't 100% be sure this was the key.
Playing with different mask types can also alleviate the issue.
Try a combination of this and report back if you can.
Welcome to the forums by the way!
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