Esta parece ser uma solução possível: link
Essencialmente, você precisa instalar os drivers no 'modo de compatibilidade do Windows XP'. Espero que ajude!
After installing Windows7 + Bootcamp drivers, you need to do a "special compatibility" installation of the sound drivers. So, after bootcamp has been installed, so the following
- Insert your original Mac OS install CD (the one that came with your MAC)
- Open the folder Bootcamp/Drivers
- Find the audio driver (Realtek or other) and RIGHT click on it -do not run it yet
- Select "Troubleshoot Compatibility"
- Let the wizard run. Choose the option "Troubleshoot program"
- Select "program ran well in previous version of windows"
- Click "test program" when prompted
- If asked to restart, do not restart yet -remember, at this point, Windows is just testing the program, so it hasn't installed yet. If you get a "restart" request at this stage it just means the program is actually ok for compatibility
- Back in the wizard, click "next"
- Wait for the drivers to install, and restart