I am 33 years old, i like to go to the borders of my fears, doing bungee jumping, skydiving, climbing (with ropes) and so on, i managed to get rid of my dentist fear and so on...so i dont think i am fearful at all.
But that doesnt change anything about it, that loud noises, spcially fireworks and all that booms that really shivers to your body because of the loudness aer painful.
The best example i can find is someone hiding to scare you. So if you are normally walking along a street and suddenly a friend jumps out yelling to scare, you normally are scared for a few seconds. Its a usual respond.
So if someone tells you, that your friend wants to scare you and you know that he will jump out of the corner you manage to prepare yourself. So you tell your brain: "He, i know you would be normally afraid if suddenly someone jumps at you out of a dark corner, but this time its a friend of me, so be prepared." By telling you that, you are able to prepare yourself, blocking your fear and when your friends jumps out you are able to control the instinctive parts of your brain, because you were able to prepare that before.
The same is it with noises. If you know befor, you can prepare yourself for knocking out this instinctive functions. It really doesnt mean i like the noises, but i am not shocked by them. I just hate them. -.-
The problem is, doing this is enduring. Imagine that your friends would decide that they want to scare you one day long. So from the moment you leave your housedoor until the evening when you come home you had to prepare yourself to be jumped at every corner, behind every door you open, behind every desk you pass and so on... doing this for about 10 minutes is fun. Doing this all day you wouldnt stand and sooner or later you get tired and even if you still knew a friend would be able to scare you, because you would still know, but would not have any longer the energy to control the instincitve parts of your brain. which means: When your friend jumps you to scare you, your instinctive brain parts would see this as an attack, starting to set adrenaline free to make you ready for fight or run.
So preparing for unusual things for some minutes is ok, its what you do when entering a ghost train. So you dont know WHAT will be happening, but you know something will be happening and for some minutes its ok. But preparing all day long for fear and terror is just making you sick. Normal people are not able to do so, why should Aspergers be able to do it, specially 5 years old?