They will get used to it. If it makes you jump DON'T stay with them. My horse has never been afraid of anything since the day he was born, he would stand at the fence and watch our fireworks, I can shoot a gun off his back, the woman who is boarding him now throws hissy fits when foreworks start going off and now he reacts like a twit. Until I give him the 'what are you doing,?' and then he looks ashamed of himself.