I have this, i think they're just getting comfortable?
I have heard that frantic movement can also be a bad sign. I think it's certainly worth a phone call. Most doctors have a after hour phone number or you can call the hospital.
I felt that with mine also. It's kinda like baby is struggling for a few seconds, like quick hard movements. It always scared me too but my doctor said as long as I feel movement it's okay it's just baby running out of room.
It's hard to say, but for sure it never hurts to be certain your baby is okay.
And it's not the hiccups I no what that fills like this is my 3d baby and I've never felt that before