Wa'alaikum assalam! Buih tu biasanya normal je kalau cara bancuh ke sikit, tapi kalau baby consistently ada bunyi kahak atau macam tersedak-sedak, I think best to check with your paediatrician to rule out any feeding issues or intolerance. A few of my mum friends pernah alami sikit-sikit buih jugak tapi disappear after a few feeds, sometimes it's just the way you're mixing or the bottle angle, so cuba ganti spoon untuk stir instead of shaking, atau tunggu few minutes biar buih tu settle before feeding.