Anxiety? Or normal fear?

My 3.5yo son is in preschool for 1 month now, and apparently he’s not mixing well or playing with other kids. He clings on with the teachers. When away from school, he is ok with older kids. He’s a happy boy btw and he can follow instructions, have very good eye contact. It’s just that he’s rather sensitive towards sound like for example musical toys or toys that makes sound, car horn, he dislike Cock-A-Doodle-Doo sound. For me, i can feel that he’s afraid of younger kids, when kids start crying or yelling, he feels uneasy and wanted to leave that place immediately. I wonder if any mommy here encounter such issue with your kids? Coz with my son, it’s only certain sound & children younger or same age he couldn’t cope with.