Same thing happened to me. I checked the console, and there are a bunch of errors loading the sounds, but I have no idea why.
This is what I see in the console:
Couldn't MovieImportDataRef (Sounds\Dominating.mp3, 7210 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\Double_Kill.mp3, 8046 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\firstblood.mp3, 6269 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\GodLike.mp3, 7314 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\Killing_Spree.mp3, 9509 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\MegaKill.mp3, 10449 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\Ownage.mp3, 10344 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\triple_kill.mp3, 7628 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\Unstoppable.mp3, 8150 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\WhickedSick.mp3, 10449 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\MonsterKill.mp3, 13375 bytes, -2048).
Couldn't MovieImportDataRef (Sounds\HolyShit.mp3, 9300 bytes, -2048).
In addition to those I find hundreds of these normal errors
WAVPlayer::SetWAVSourceImmediate: Failed to open [Units\NightElf\AncientProtector\TreantAttack2.wav]
WAVPlayer::SetWAVSourceImmediate: Failed to open [Units\NightElf\AncientProtector\TreantAttack1.wav]
WAVPlayer::SetWAVSourceImmediate: Failed to open [Abilities\Weapons\WitchDoctorMissile\WitchDoctorMissileHit1.wav]
WAVPlayer::SetWAVSourceImmediate: Failed to open [Units\Creeps\HeroFlameLord\FireLordMissileDeath1.wav]
I wonder if it has something to do with any quicktime plugins that are installed. Do you have any installed like Flip4Mac or DivX?