Movements other than kicks and hiccups?

I'm about 28 weeks. From yesterday, I've been feeling a new sensation in the lower part of my womb, near my private part. I don't know how to explain it but it's like a very subtle weak constant vibration, nothing like kicks. I felt it like over 10 times today. Each time it lasts for 1-2 minutes. What could it be? I don't think it's hiccups either.