If you only have the Monitors and Sounds control panel, you may want to install the Sound control panel.
Do the Sound control panel's Sound Out sample rate and resolution settings match the ones set in Peak? To check, select a portion of audio in Peak, choose the Audio Info command from Peak's Preferences menu, and note the settings. Then, open the Sound Control Panel from the Apple menu, and choose Sound Out from the pop-up menu. If the settings don't match, correct them here. (This may also cause the system beep to play at the wrong speed.)
If you are using a plug-in audio card such as Digidesign's Audiomedia II, the input source or clock rate may be set incorrectly. Make sure that both of these parameters are set correctly by opening the Macintosh's Sound Control Panel and choosing Sound In from the pop-up menu. This problem is very common if your audio card is connected to a digital recorder and is receiving its clock rate from that device. To avoid this problem, always set the input source back to line or line + mic and set the Sync Mode back to Internal in this dialog after you have finished transferring audio digitally. If the file plays back about 10% slow or fast after switching from digital to internal sync, the sample rate selected in the Hardware Setup window may not match the sample rate of the digital source.