I’ve noticed this year when I run up my two flights of stairs at home my heart will be racing so hard it actually starts vibrating, it feels like I have a mobile phone buzzing in my chest. It only happens when my heart is beating really really fast. It stops after a few seconds but it’s horrific and it scares me

My doctor said it sounds like Palps and if I’m not feeling faint, having chest pains or actually fainting she isn’t concerned.
I’ve had two normal ECG’s the last two months and I had a chest X-ray and no one said anything about my heart appearing to look weird. Has anyone had this vibration feeling?