Vibrations during meditation is a normal phenomenon and nothing to worry about. Every matter in this universe possess some energy and has some frequency of vibration. We are enwrapped in an energy field.
As your body starts to relax during meditation, the movement of energies are felt as vibrations. This is a temporary thing. As you progress the vibrations goes off and you become stoned. Do not focus on the vibrations, just observe and Let Go!!back