I hear people describe different arythmias as a vibration. I know one person described a-fib like that. Obviously theres no way to know without it being captured on a holter. If you get it daily, a 24 hour holter should be fine but if its rare, a 30 day event recorder would be needed. You need to see a cardioloigist to be safe. If its afib you would need to be on some sort of blood thinner. Please call your cardiologist. Another thing to consider is calling a pharmacist or researching to see if the medication you are on can cause any heart rythm issues.
Is the vibration more systemic, through your shoulders and upper arms or is it centered only in your heart ares?