Did you check that your sound output is set to be your sound card rather than your AV device? I don't have PPro fired up at present but, from memory, there's a drop down box for your playback window where the option exists to choose where you want sound to go.

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Premiere Pro, Encore, Photoshop, Ulead VS6, WXP Pro, Core 2 Duo, 2GB, 2 x 250GB SATA3 drives, 2 x 250GB USB 2 external drive, DVD writer, GeForce 7300 GS 256MB

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