Toddler wont go potty in public?

My daughter will be 3yrs old in Oct . Shes great at home going potty she wears toddler undies and everything. But when we go to a store she'll say she has to go potty . But once we get to the bathroom she starts screaming and cry . She is afraid of the tiolets flushing cause they are too loud. Idk what to do. Cause i cant control how loud they are. Then sometimes we have to put a diaper on her cause we are to far to run home. What can i do to make her not afraid cause shes doing so well at home. Also she does stay home with me , doesnt go to daycare or anything.