Disable the MMCS but Make sure you read the whole text.
Windows 7 Ping Spikes [FIX]
Windows 7 - "lag" in online games with Windows 7
My optimal solution was to keep the MMCS service running, as if you turn it off your audio may start cackling/skipping in an annoying fashion. However, I disabled the network throttling component of this service. I believe it's a general audio problem specific to Windows 7 and multiplayer / online games. I don't think the audio card or the drivers make a difference, or at least they didn't in my case.
Leave the multimedia class scheduler service running, but disable its network throttling feature:
* Open regedit
* Go to: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Multimedia\SystemProfile
* There will be an entry for network performance throttling, default value is 10; set it to FFFFFFFF hex (willl look like 0xFFFFFFFF to the right of the entry)
This removed the lag I was experiencing while still enabling me to have normal sound in-game. Specs in profile.