Moondrop is made from Aluminium therefore it has a soft metallic ''click'' sound when slider hits the end point. We really love it and it's actually one of the most satisfying things when fidgeting with Moondrop. It also distinguishes Moondrop from the cheap plastic toys out there. However sometimes there might be situations when you need to be absolutely quite but still want to fidget -  important meetings, lectures, etc. 
For those situations we have created special silicone O-rings. Whenever you like just put them on and they will silence the ''click'' sound. Four O-rings will be included with each Moondrop. 

You can keep the o-rings in the small groove on Moondrop while not using them and put them on whenever you need the silence.