My coming to 21 months girl is afraid of noises. To the extend of me calling out my 7 yo boy from my room to the living room, she would just jump up and panic and cry and say she is scared. Some times when she is taking her nap , someone comes home and call for someone, she would also wake up and panic. We are quite sure that she wasnt scare by anything in her life. What can we do to help her overcome this issue ?

Have you considered if your girl has hypersensitivity to certain noises? My elder girl has since young been very sensitive to loud noises - like the cymbals of a lion dance troupe, fireworks, and the likes. But the fun loving nature of her helped in a way to overcome this by not being distressed as she grows older, but instead she learns to cope with it. We helped her along by telling her in advance what to expect. We reminded her that she can cover her ears, or we could leave if she really couldn't stand it. 7 years old now, she still has anxiety over loud noises, but she's now learnt how to manage it better. She didn't want to avoid expected louder places either, because she couldn't bear to miss the fun! We have come a long way with her and one of the earlier things we did when she was younger, was introduced white noises to her when she slept. Somehow white noises calmed her during her naps and she was less startled if rudely awakened by any unexpected loud noises. You may want to try it too? Be more conscious of her reactions and always be assuring but not negating her anxiety because they are real. If you Google sensory processing issue (particularly noises in your girl's case) you will find many resources as to how to better cope or overcome the anxiety. Some good tips from this website but I'm not sure if these work for your girl as much as they did for mine. Do consider: https://www.understood.org/en/learning-attention-issues/child-learning-disabilities/sensory-processing-issues/7-ways-to-help-your-child-cope-with-noise-sensitivity#slide-1