I still think/hope it's a bug. I can't hear it at all unless I turn the volume way up. It should be the same volume as the other environmental sounds. I cannot hear anything splashing around in the water like I used to.
I have the same problem. All other sounds play at normal volume but when I jump into any pool of water the splash sound is VERY faint. In my mob trap, skeletons splashing in water make almost no sound. This appears to be limited specifically to the water splash.
I still think/hope it's a bug. I can't hear it at all unless I turn the volume way up. It should be the same volume as the other environmental sounds. I cannot hear anything splashing around in the water like I used to.