Baby hearing

I pregnant 29weeks now, today a sharp thunder scared me, but my baby no reaction. Last month people throw cartoon box, I feel the sound so loud, I got scared, but baby no reaction. I heard people say baby can hear in the womb, they can react to a sudden loud sound. But my baby seems block all the loud sound, never react on that. Is it normal? So worry if he is having hearing problem. What I should do?