1.) (Best) Go to your Start -> Run -> dxdiag and click on the Sound Tab. Then in the Hardware Sound Acceleration Level move the slider all the way to the left to disable hardware sound acceleration. This completely solved all my sound problems in both Might & Magic 6 & 7. Be sure to move it back when you want to play other games, like Heroes IV.

2.) Or once you are in the game itself, you can hit the Esc Key, choose Controls -> Sound Options (not Voice Options) and move the slider all the way to the left so that all sounds will be disabled in the game. This works too but, obviously it's a big hassle and you don't get to enjoy the sounds of the game.

Good Luck & Have Fun!