Abdominal muscle spasms?

Hi all,

31 weeks pregnant, all has been healthy and smooth so far. In the past week or so, I've started experiencing a "pulsing" that feels like tiny muscle spasms in my lower stomach region. Very different than the sensation of baby moving. Some days it last for hours. Not painful, just distracting lol

I'm not concerned about it being a problem... I'm just curious about what it is! And my googling hasn't shed much light, except for possibly the start of Braxton Hicks? 

Anyone experienced something like this or know what it is? Thanks!! -Emily