As far as I know,Creepers aren't supposed to have idle sounds, but in 0.16.0 beta they make their damage sound as idle.
MCPE-17257
Creepers use their hurt sounds as idle sounds
Resolved
Fixed
2
(Unassigned)
34386
Confirmed
Phone - Android - Samsung Other (Specify in description)
Android 5.1.1
creeper, sound
0.15.90.7, 0.15.90.8, 0.16.1
0.17.0.2
Retrieved
This is a bulk resolve of issues that haven't been updated to 0.16.0+ yet. Please comment below (To open the ticket) and update your affected versions. If you cannot reproduce the bug, please write in the comments so we can resolve it as "Cannot Reproduce". Thank You!