Hello, as previously mentioned (thanks, @Darwin), I am an Audiologist.
@Harp‘s response is interesting as to the possible reasons why these reflexes developed. But for whatever reason, we all have them. However, as with most body functions, there are variations of ‘normal’ and then at the extreme ends there are abnormalities of too much or too little.
Some people are more sensitive to loud and/or screeching sounds than others might be. That sensitivity might just be an idiosyncracy, or it could be a sign of other problems – usually with a neurological basis. Some autism-spectrum disorder patients have hyperacusis. Some hearing impaired patients have recruitment. Some patients have sound sensitivity as a migraine aura (with or without headaches). And some patients with anxiety or PTSD are very jumpy. There are rarely some people who get vertigo attacks from loud sounds.
The only way to know if your sensitivity might be attributable to another medical issue is to have your specific symptoms and history reviewed by a qualified professional, ideally a neurotologist (‘neuro’=nerves, ‘oto’=ear), who will include a comprehensive audioligical evaluation as part of the test battery.
In the meantime, you might consider wearing mild attenuation musician’s earplugs that can lower the volume around you by 9 or 15dB. The most comfortable are custom molded to the ear, and don’t hinder most normal conversation (assuming that your hearing is normal). If you do have hearing aids, the settings in most digital aids can be adjusted to
lower maximum outputs to keep sound comfortable for the wearer. Some Manufacturer’s claim to have engineered circuitry to better manage those sudden loud sounds more effectively.
I hope this helps, and will gladly discuss this further if you’d care to post more specifics.