there's a strange heartbeat/pulse in my belly

I know it's not my baby's heartbeat because it is slower than what I hear when my baby's heartbeat is read at the doctors office, I also know it's not my heart beat because the rhythm doesn't flow with my heartbeat when I try to listen to both. Please who else experiences this? It's becoming quite frequent these days! I'm 32weeks... does it have anything to do with how far long I've gone? I'm confused 😐