When we begin to use mantra it can be quite uncomfortable. Hearing the fear or any other uncomfortable feeling that may resurface means that they are ready to be healed. The vibrations in the words you choose will connect you with parts of yourself that may need to be detached in order to heal. This is why connection to the vibration of your mantra is so important. The vibration will bring to the surface the parts of yourself that are ready to let go. Then all you need to do is let go!
See blog How to connect to the vibration of your mantra to learn how to connect with the sound vibration.