If you quickly get out and back underwater before the already playing underwater loop stops, it will play another underwater loop sound along with the already playing ones.
The F3 debug screen will show that in x/8 under sounds, x will increase as you continue quickly getting out and back in.

Expected behavior
When going over and underwater quickly, only one underwater loop should be playing at once.

Actual behavior
Another underwater loop starts playing and the already playing ones don't stop.

How to reproduce
Go underwater and quickly get out and back in, you can try swimming through a door underwater.