When you feel anxious, panicked or even very excited, your body prepares itself for action in what is often called the ‘flight or fight response’. This response is very useful in ‘survival’ situations which our bodies have evolved to cope with - it temporarily makes us stronger, faster and more resistant to pain - which is pretty handy if you're being chased by a bear or hunting a wild boar (though not very useful if you're giving a presentation in the office boardroom).
One of the features of this response is increased heart rate - to pump oxygen-rich blood to your muscles - which you may detect as pounding in your chest or, in your case, the sound of the blood vessels in your ears pulsating. It's completely normal and nothing to worry about - just your body's way of preparing your for action.
If it bothers you, you could try a breathing technique to relax your body and reverse the stress response (see link below). But don't fight it - struggling only makes it feel worse and you'll just end up feeling worried about feeling worried, or upset about being upset!