I recently had dodgy sound issuse like this.
If you paused the music for a while did it go back to normal?
If so it could be a problem with your Hardware Acceleration.
Try going to start >> run >> type "dxdiag" (with out quotes) >> in the dialog that appears find which sound tab refers to your sound hardware (most likly sound 1) and make sure the Hardware sound acceleration slider is set to full acceleration.
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