I know this! It has the delightfully onomatopoeic name of borborygmi. Basically, your tummy is always rumbling but when it is full of food, the sound is muffled so you can't hear it. When your stomach is empty, the sound reverberates in that embarrassing way. I've not heard of it being a sign of weight loss but as your body will HAVE to burn fat if there is no ready source of energy, then it makes sense.
Hope that helps!
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