Dopplers will not affect the baby, it only mirrors the sound from your tummy. HINDI totoo na may radiation siya, if may radiation man it would be illegal to sell it carelessly online. Di siya recommended ng OB just because you might think the baby is okay kasi may heartbeat but in distress na pala si baby.
Anyway to answer your question, parang bubbles sa loob ng tiyan daw. I have yet to experience it since I’m only 15 weeks in.