If you go to the Nether and move/look around for a bit, sometimes you may hear ghasts making very high-pitched noises than normal.
It's not always the case though, as they do make normal sounds as well.
MCPE-34572
Ghasts sometimes make very high-pitched sounds.
Resolved
Fixed
6
(Unassigned)
126049
Confirmed
Phone - Android - Samsung Galaxy Note 5
Android 7.0
ghast, high-pitched, sound
1.6.0.1
1.6.0.5
Retrieved
Should be fixed, according to the 1.6.0.5 changelog.
(Mobs no longer play a higher pitch sound effect when first spawned)