Dogs have much more sensitive hearing than humans, so they can hear sounds that we can't.
Dogs who have had a negative experience with a loud noise, such as being caught in a thunderstorm or being injured by a firework, may develop a fear of loud noises.
Some dogs may be more genetically predisposed to noise phobia than others.
Dogs who are not properly socialized to loud noises as puppies may be more likely to develop a fear of them later in life.
Some medical conditions, such as hearing loss or pain, can also make dogs more sensitive to loud noises.
Expose them to loud noises gradually. Start by playing recordings of loud noises at a low volume and gradually increase the volume over time.