Eh, normal je tu! Dekat 21 weeks, baby's heartbeat sudah kuat and sometimes you can feel it pulsing, especially kalau dia positioned low or in front. A few of my mum friends describe it exactly like what you're feeling, macam ada second heartbeat je. The movements at this stage pun memang varied, sometimes feels like kicks, sometimes like flutter, sometimes like a denyut2, so don't worry! But just to be safe, mention it to your gynae during your next checkup, okay?