Ear guards is a good idea. Always make sure you have your horse in front of you because when the horse look spooky around -and you have a contact to the bit you can easily press the horse with your legs in the right position again.
Ear guards could help, but experience is the best cure. Take him to shows ALL the time, even if you're not competing. Riding around in the atmosphere will teach him to relax.
Try to do some desensitization Before you begin riding. I had the same problem and desensitization really helped
Maybe try earplugs so he doesn't get distracted by outside noises