What am I feeling?

I’m 26 weeks pregnant and a few times a week I will feel a consistent thump in my lower belly that will be perfectly timed every 2-3 seconds apart for about 3-5 minutes. It’s not like normal kicks, it’s more just thumping in the same spot every time. Is this the baby having hiccups? Just muscle spasms? Sometimes it’s annoying cause it’s so constant lol! WHAT IS SHE DOING IN THERE?! 😅