[Galaxy S8/S8+]sound is not clear with crackling noise after being exposed under water.

If the device has been immersed in water or speaker is wet, sound may not be heard clearly during a call because water may get in the speaker hole during exposure underwater.

At that time, please wipe the device smoothly with a dry, soft cloth and allow to dry thoroughly before using the device.

For faster drying, try using cool wind and/or shake the device smoothly a few times whilst holding
the speaker face down. 

Despite this, when some moisture remains on Mesh in front speaker, sound may not be still heard clearly.

At this time, as this moisture can be also removed by speaker vibration during call, please check
the device’s sound state while making call for a period of time.

If you are still having trouble with the sound after trying these tips, please contact a Samsung Service Centre.