I think the consensus is that it is plausible. It depends on the range...100 yards, possible, 50 yards not likely, 25 yards and the target wont hear the shot.

In order for you not to hear the shot at all, I think most likely the shot would have to be brain-penetrating, and enter at a higher velocity than the speed of the nerve impulses from the inner ear (which isn't hard since nerve impulses actually don't travel very fast). :)

As far as knocking someone across a room.... let's remember simply physics. Every action has an equal and opposite reaction. And since the projectile loses energy due to air drag, it actually strikes the target with less force than the recoil that the shooter feels. Any shot strong enough to throw the target across the room would do the same to the shooter.