Quivering feeling in womb. 3rd Trimester!

This is my second pregnancy, and I'm 30 weeks today! For the last couple of weeks from time to time I'll feel the baby (what feels like) quivering or vibration or a seizure like feeling that only lasts 2 seconds or so. I never felt that feeling with my first son. All of my tests and ultrasounds have come back normal but still wondering if anyone has ever experienced this feeling. Is it normal? Please ease my mind!