I don't know if you fixed your buzzing sound yet but I did. I have an Audigy II Platinum Plus sound card. This all starting happeneing when I installed the CCCP codec pack but I don't that is the problem for this reason. Well, who knows where the problem REALLY is since it's all beta software. Here is what I did to fix it.
Pretty much just installed the
driver Windows offered. I removed the SB Audity entry from the device manager list including
drivers when asked > uninstalled all the Creative software from add remove programs > reboot as asked > Went to MS Updates in contol panel > scan for updates > click on 'optional updates' (Option was there for me) > installed the
driver from MS > rebooted when asked > and I"m now able to play DVD's with Windows Media Center 7.
Haven't tested MKV playback yet but I will. I want to watch Barry Lyndon badly. I hope it works out.
UPDATE:
Actually, I just uninstalled the Windows SB Audigy
driver and reinstalled the vista driver from the Creative website and the sound still works ok. So, for me, it was something w/ the CCCP Codec pack (probably ffdshow). So I'm not sure what to tell you guys. But maybe this will help you in some way.