Not sure, but i think that waht i have been getting are these also,,,, The bubs gets hiccups heaps,, and it is definetaly not those,,, it is not my own heartbeat,,, or my breathing, as I can time that and just hold my breath, and it is still there. you can actually see my belly rise and fall in a rythmic movement,,, right over bubbas back. I was thinking it must me bubba practising breathing also