Hiccups probably that happens to me as well.
My stomach visibly pulses all the time, pregnant or not! Probably your own heartbeat, but could be baby hiccups as that's very similar but actually ends at some point, whereas obviously your heartbeat (you hope! will keep going ;)
There is a big vein (of yours) in your stomach, and it pulses. You would not see his heart beating, since he is enclosed in a bag of water.
No it's probably either your heart beat or hiccups. I can see a pulse in my stomach and I'm currently not pregnant.
Could be kicks or if they were pretty evenly spaced it could ce hiccups