I find that after 1-2 hours of use the firewall’s DPC Latency goes quite high (4-6ms) whenever there is network activity. This is fixed by uninstalling the firewall component of Avast.
I recently started to experience choppy audio playback on my Windows 7 desktop PC. After much searching I learned that Avast Firewall can cause large DPT Latency (up to 20 or 30 milliseconds in my case!). I uninstalled the Avast FireWall feature, and now DPT latency is down to the <1ms range where it belongs.