Having had this issue myself and reading on this board about others with this problem, I thought I'd post my fix to the issue where the voices are clipping and/or pop.
I tried the usual by updating the drivers for everything, but the problem persisted. The only way I got it to stop was by going into the control panel and lowering my sound hardware acceleration down to basic. This removed all sound problems from the game. I don't know if it will fix anybody else’s, but I'd thought I would throw my solution out there.
For those who might need it spelled out a bit more clearly:
Go to your Control Panel
Click on 'Sounds and Audio Settings'
Click on the 'Audio' tab
In the Sound Playback box, hit the 'Advance Settings' button
Another window should pop up. Click the 'Performance' tab.
Drag the 'Hardware Acceleration' slider until it's at 'Basic Acceleration' or the second spot from the left.
Hope this is able to help someone.