I learnt that babies do feel insecure when there is no sound around. I was surprised at this.
My son's doctor says, inside the womb the babies are used to listening to high decibel sounds. After born they feel alien to be in quiet surrounding.
He also advises to carry the baby 36 hours :) a day. This makes the baby feel secure. Immediately attending to baby's cry is important as it increases self worth in him.