Hi,
This should be a driver issue. The driver update may not be installed properly. I suggest that you remove the driver, and then run Windows Update to install it again.
How to remove.
1. Click Start. In the Start Search box type "devmgmt.msc" and press Enter.
2. Expand "Sound, video and game controllers", double-click on the entry of the sound card.
3. Click the tab "Driver", click "Uninstall".
4. Click Start. In the Start Search box type "appwiz.cpl" and press Enter.
5. Remove the entries related to the display adapter.
Then, I suggest that you temporary disable the anti-virus, then run Windows Update to install the audio driver.
Please understand that Windows 7 RC is for test. The drivers on Windows Update website were released by hardware manufacturer. Microsoft has tested these drivers and involved them in Windows Update. However, since currently the whole system is for test, the audio driver may be not fully compatible. It just help the device to work, but the performance may be not perfect. If the issue persists after reinstalling driver, we may need to wait for new compatible driver from hardware manufacture.
Arthur Xie - MSFT
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