Wah, understandable lah worry macam tu first time! Bunyi nafas bayi masa tidur memang boleh jadi scary, tapi yang penting is kalau dia breathing normally (tak laboured, tak pull in ribs) and colour okay, usually it's fine je, babies make all sorts of funny sounds masa sleep because their airways masih kecil dan sometimes ada phlegm. Tapi since you're concerned about the sound specifically, best lah you mention it to your pediatrician next visit or call them just to get peace of mind, they can listen and confirm everything's A-okay. My mum friends and I pun dulu paranoid gila about every sound!