Why Am I Getting Low Vibrations In My Heart Area?

I am getting low vibrations in heart area in my chest like the ringing of a mobile on vibrator,it is not causing any discomfort . Has occurred 5-6 times in last 9 hours. Each time 5-10 seconds. First I thought the mob is in my pocket. But it was not so. It was far off and no call has also come at that time. I am active person doing yoga 4-5 times a week and walk 6 days a week. Diabetic but sugar under control