Being unable to mute the sounds isn’t really something I enjoy, I am using the HTML 5 beta, so i’m only hoping this wasn’t intended as there is still a mute button, just doesn’t work.
For those who play using the HTML 5 version and don’t already know this, use the chrome tip for making the html 5 client as seen here : Quick find code: 334-335-412-64932128
Once you’ve done this, you can go into system sounds (Bottom right, the sound icon usually next to the network icon) then select > Mixer, then mute the Runescape 3 Gold one, although you’re running this client through chrome, it’s running completely separately, thus it only mutes Runescape and not other chrome processes you’re running, such as youtube, netflix, whatever.
Alternatively if you need to hear sounds but want to do other things, just turn the volume down so you don’t miss important sounds / speaking characters.
If anyone doesn’t know this, i’d be surprised, but i thought i’d post nevertheless.