Two local proxy problem... if so, it is possible that this causes my sound chattering (only sometimes, indeed), because I use another local proxy (Proxomitron).
My sound chattering is always on my PC (long running worsens this), and avast! and Proxomitron is always together too... I thought chattering is because my PC's power shortage, but it seems this is the reason.
Now DPC Latency Checker shows exactly same graph compared to before my post, and this time is only 1 hours after reboot (with no P2P application).
Cako, are you using other local proxy software? If so, it can cause your problem too.
Anyway, I like avast very much. Thanks Vlk for your great work!