At this point, your baby gets startled and cries at loud noises as these sounds are not familiar to him. He is not able to identify the source of loud noises. These uncertainties cause fear and he cries. However, this phase is temporary and disappears when he gets familiar to different sounds and can identify the source.
When your baby gets startled because of loud noise, just pick him and say, “That was loud! But it’s okay. Everything is fine" and hug him. Through patience, perseverance and exposure, you can help him overcome fear of loud noises. Your baby may get startled while sleeping, don't worry that is normal behaviour. He will develop his startle reflex soon.