Hmm, that vibration feeling could be Braxton Hicks contractions (practice contractions), memang lain dari baby movements, lebih macam trembling/tightening je, especially kalau ni first time pregnant. A few of my mum friends mentioned rasanya macam geli or vibrating sensation around that stage, but I'd suggest tanya your gynae to be safe, especially if it's consistent or discomfort jer. Usually it's nothing to worry about, but better confirm dgn doctor so you're at peace of mind!