from Microsoft:
Troubleshooting Audio Playback Issues in Windows Media Player
Why does my music sound like chipmunks are singing?
Don't worry, small rodents haven't set up housekeeping in Windows Media Player. Instead, your sound card's clock most likely has a timing problem. To fix the problem, try reducing the hardware-acceleration level for your audio card by doing the following:
1. In Control Panel, open Sounds and Audio Devices.
2. On the Volume tab, in the Speaker settings area, click the Advanced button.
3. In the Advanced Audio Properties dialog box, click the Performance tab, and then adjust the Hardware acceleration slider control to adjust the clock timing for your sound card.
Keep in mind that, if your sound card supports multichannel (5.1) audio playback, turning off hardware acceleration (by moving the slider to None) will cause the sound card to play all multichannel audio in stereo (two speaker) sound.
If you can't fix the problem by adjusting hardware acceleration, check for updates for your sound card by doing the following:
•Check for sound-card driver updates. You should scan for updates on the Windows Update Web site and
also check for updates on the Web site of your sound card maker.
•Check for Microsoft DirectX updates by scanning for updates on the Windows Update Web site.
http://www.microsoft.com/windows/windowsmedia/knowledgecenter/mediaadvice/0067.mspx
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