I think it sounds like movement.
I had my first few flutters at around 16 and a half weeks and they got stronger and more frequent.. now they are definately kicks as you can see my stomach move or feel it when you put your hand on it. My best way to describe it to the girls at work is like when you have gas but the feeling is on the surface of your tummy and around your uteris area. (sorry if TMI). My bubs is extremely active, even shown on his scan, so i get kicks most of the day.
I know how exciting it is to feel those first few kicks!