It’s perfectly normal for a child to feel scared during this age. With so many experiences and new abilities acquired every day, this feeling develops so the child can learn how to deal with potential dangers (at least from a child’s point of view) and how to protect against them.
This way, nightmares can happen in the middle of the night, even though the child might not be able to verbalize exactly what they were dreaming of. Clowns, dogs, insects, the dark, loud noises, masks, costumes…All of this can frighten the child. And, also, new situations or different people.
This fear will go away as the child grows up, but this process sometimes may take time. But, that doesn’t mean you should ignore their tears and discomfort. Laughing, for example, is something to be avoided. Even though your child’s fear seems irrational and baseless to you, to them it’s a very real threat.
Ideally, you should show the child you understand what they’re feeling and that it’s a completely valid emotion. And, whenever possible, explain the reason for a loud noise: “the ambulance is driving by quickly because someone inside is sick”. Or, you could even try helping them face the “terrible” situation, such as walking by a clown or dog they’re afraid of.
Books about whatever is triggering their fear – witches or dinosaurs, for example – might help during this phase.