One can set any of the volume sliders to 0% (not OFF but 0%) and sounds will still play.

To recreate, slowly move the Volume slider towards OFF. One may notice that the slider can sit in between volume OFF and 1%, showing 0%. Then just check the game volume and notice how it still plays sounds.

Note, this was first tested and screenshotted whilst playing modded version OptiFine HD U G9 pre17, but same behaviour occurs in official release 1.17