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Could the rattling sound be purring?
Is there any chance she aspirated some milk?
Any coughing or sneezing?
Is she eating well and gaining weight?
Did she ever get any mothers milk or has she been bottle fed from birth?
After your reply please give me a few minutes to type detailed answer.
If the baby is eating and eliminating normally and gaining weight, I would not be overly concerned about this "rattle".
Going to sleep means she is feeding well and happy.
The noise may be the milk going through her GI tract or an early purring reflex.
If (God forbid) a kitten aspirates formula, there would be coughing, breathing difficulties and fluid in her lungs.
Please let me know if you still have questions or wish to discuss this further.
I hope the baby will be just fine.
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