#noises

Is it normal for my 6yo to get anxious from loud noises, specifically, fire alarms?

My son is 6 years old and ever since he started pre-k he has been scared of the fire alarms. He hates them. It causes him anxiety. It was worse when he was younger but even after a year or so of being in school he still hates them and gets anxious. We talk about it often and tell him what they are for but he still does not like them. Today the teacher wrote to us that he has been covering his ears the past few days and today he said he had a headache and we suspect it's because the school administrator told him this morning there will be a fire alarm. We asked the school admin, at my son’s request, to let him know the day there would be fire drills. Is this normal after so long in school, what else could we tell him?