Question

why are we not able to hear the sound of Dreams ? Danny's father

Answer 1

It only happens sometimes.

While you're sleeping, your entire body is paralyzed except for your eyes (that's why its called Rapid Eye Movement) and your breathing. This is to stop you from acting out your dreams. But sometimes the paralysis isn't completely flawless. That's why things like this can sometimes happen:

https://www.youtube.com/watch?v=CeKGgzDJZvs

So this is just when your ears aren't properly paralyzed and your real body's ears can hear things in the real world.