1sec system freeze when streaming audio / video from network

I got COMODO Firewall V on a Vista x64 Machine (Intel Q6700; 4GB RAM).
Since i installed the firewall i experienced hickups when streaming media over the network. I first noticed it with winamp, because i access my mp3-files over a networkshare on my local machine to be able to use the same playlist on different machines in the network. But now i got the same stutters when streaming from youtube. Not only the player freezes for about one second, but the whole machine stops doing anything. WMP stutters when streaming over the network, too.

At each stutter 2 of the four cores rise to 50% loadout each. (seen it in my sidebar gadget)

My first thought was it could be that im running folding@home-smp-client, which uses MPI to sync up, but the sound still stutters after shutting down F@H (mpi stops then, too). Even shutting down Comodo didn’t change anything, but since i first experienced it right after installing Comodo and rebooting, i don’t see another reason. I already increased the stream buffer to 4 seconds, but since the whole machine freezes, this doesn’t help.

Defense+ is disabled, Firewall is in Training with Safe Mode.

Applications running, too:
Truecrypt (the disk i stream from is encrypted)
Logitech SetPoint
Avira Antivir
Daemon Tools

I hope you guys can reproduce my problem and help me out.

Thanks a lot