I know this thread is old, but I want to help other people with Avast/audio/DPC latency issues. Plus, Mut@nt's observed behavior, especially the DPC latency monitor captures, are identical to mine: green on restart (especially using the ipreset.bat tool), then some yellows, a red or two, then all reds/yellows or greens mixed with reds through the roof, all over the course of hours or days. So I'm replying to it rather than starting my own thread. I want to present a solution rather than an issue, anyway.
I had serious audio pops, which were the symptom I was trying to stop. The problem started around September 2013, when I upgraded from Avast IS 2013 to IS 2014. Every other thread I found by searching on audio+DPC+latency either found other hardware/software-specific issues (USB, graphics, net adapter) or failed to solve the problem at all. After applying a half-dozen partial fixes and optimizing my network to perfection, I decided that tcpip.sys was the worst offender and demanded my full focus. Eventually I was led to also search for "ping spikes," ran a continuous ping and observed that ping spikes corresponded with major latency spikes, and then read that antivirus port scan detection could cause these spikes. I turned off Avast and got the same results as Mut@nt.
Turning off Avast, specifically the Avast firewall, specifically "enable port scan detection," stopped this behavior utterly. I tried this only after testing everything else: power management, IRQ conflicts, USB net adapter disabling, disabling unneeded drivers, preemptively disabling PowerMizer, running TCPOptimizer, and so on. However, I'm not saying this is a general Avast issue---it is very likely that it's some other hard/soft combination that responds badly to the Avast ndis filter scan. It may be that a PCIe card would solve the problem for good, and it may not.
One feature of my network setup is that I'm using a Verizon router as a bridge to a Dlink DIR-645, which becomes the network's wireless access point. It's possible this messes up what Avast does.
Operating System
Windows 7 Home Premium 64-bit SP1
CPU
AMD FX-4100 67 °F
Zambezi 32nm Technology
RAM
16.0GB Dual-Channel DDR3 @ 802MHz (9-9-9-24)
Motherboard
ASUSTeK COMPUTER INC. SABERTOOTH 990FX (Socket 942) 110 °F
Graphics
H233H (1920x1080@60Hz)
1023MB NVIDIA GeForce GT 520 (Gigabyte) 103 °F
Hard Drives
466GB Western Digital WDC WD50 00AAKS-00D2B0 SATA Disk Device (SATA) 94 °F
932GB Western Digital WDC WD10 EADS-00L5B1 SATA Disk Device (SATA) 92 °F
1863GB Western Digital WDC WD20 EZRX-00DC0B0 SATA Disk Device (SATA) 87 °F
Optical Drives
ATAPI iHAS124 B SATA CdRom Device
Audio
Realtek High Definition Audio