Ghasts don't make their "ambient" sounds or the sound when they launch a fireball. They do make these sounds in the java version.
Ghast are annoying mobs, but it's even worse when you can't tell whether there is one close and if it's shooting at you.
They do make a death sound though.
Linked issues
is duplicated by 4
Comments 4

This bug has been reported to our internal bug tracker for further testing and a fix. It is scheduled to be fixed in one of the future updates (no specific date can be provided).

Please reply and update affected versions if you're still able to reproduce this issue in 0.17.0.2.
Cannot repo this issue as of 1.0.0.7
This is also happening in the Android version.
The issue is that they are making sounds, but they're following the normal sound proximity rules. You can't hear them unless you either crank your volume up, and even then they have to be just outside of melee striking distance.
Right now they're like creepers that can fly and set you on fire without dying. This is making trips into the Nether even for careful, seasoned veterans to search for fortresses, wart, and blaze rods a complete flip of a coin as to whether you're going to make it back without losing your materials.