I have a xonar and I get a split second noise after quitting, its not awful or anything.
Disable GX in the Xonar control panel.
Re. the issues with the Sabo'. No I don't think they need nerfing. Sure they have huge damage potential but this is offset by them not dealing any damage until they detonate.
I might be playing the class a bit wrong but I go down pretty quickly if I get caught. The high number of killing blows comes from timing your detonate to when you know (or have a fair idea) that your detonate with take the target's remaining health past zero, nothing more.
One of my guild mates is a higher level Sabo than me and is getting creamed by Warriors and can't overcome the heals of some high level Clerics.