dreamcast running fast

I just bought a Dreamcast with Sonic Adventures. Most of the time when i play this game the sound and music plays at double time so that everyone sounds like a chimpmunk. Have you heard of this before and do you know how to fix it. Music cd are the same

[webber]

if it is brand spanking new and the original disc bring it back immediately, no questions asked it is either the disc or the hardware

regards
webber