Default set system sounds near silent

hi^^
I have a problem, using a lot my earplug. the thing is, when I listen to music and a system sound comes, it blows my mind away. .. could I disable this sounds, or better, just decrease the volume? I don't need this sounds, okay , sometimes they are helpful, but mostly it's just annoying.. I think there must be a registry entry to change that, shouldn't it? thanks for your help!!
greets, cad