I've been getting the same thing. Like a little pulse or something. I think it's probably kicks or punches and they are just stronger. I think the flutters are probably either him moving or lighter kicks/punches. I don't know this, just my theory. It sure feels great though, doesn't it!!
Well, it's kind of hard to say that it is 100% the hiccups, since everyone feels things differently. Mine felt like little rhythmic 'bumps', almost like your own hiccups from the inside if that makes sense.
What did your sons hiccups feel like? Didn't sound like you were sure if it were like my sensations.
It very well could be hiccups. My son had them all the time. :)