soft-sliderslide.wav and soft-slidertick.wav are silenced, actually these files is used at 00:04:954 (5) - .
Hitsounds from notes and sliders must be audible. These provide feedback for the player, and having them silent in a rhythm game doesn't make much sense. If you don't like the default sounds, then find replacements rather than silencing notes. You can use hitsounds from the Custom Hitsound Library or easily find others online. Lowering the volume of a few notes to provide a dampened effect is usually fine, but complete silence is always unacceptable. The end of a spinner (or even the entire spinner) the sliding sound of a slider, and the end of a slider can be silent, but only do it if it makes sense. Finally, you cannot silence both slider ticks and slider slides together.