Because this is a shared computer I have many users, and in one of them (the one is mine) the volumen is too loud. I don’t know is there a place to turn the volume low.
This happened since one I use the VNC client. I don’t knwo if this information matters but just in case.
I’m not familiar with VNC, but perhaps you’re adjusting the wrong user account audio settings. Or maybe it requires adjusting via alsamixer from a root terminal?