Is Sound Manager version 3.0 or later installed on your Macintosh? If not, you must install this Macintosh System software. (Note: Sound Manager is automatically included in System 7.5.)  * Is AppleTalk on? If so, use the Apple menu's Chooser to turn it off if you don't need it.
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.
Try increasing the playback buffer size in the Playback Preferences dialog. (Always use the smallest working setting, though, because this setting also affects how much memory is used per window.)
Apple System 7.5.3 is reported to cause problems with various types of digital audio systems. This is a result of the new native SCSI Manager and only happens on Power Macintoshes running 7.5.3. This affects all digital audio programs. However, most 7.5.3 PowerMac users are not affected, and 68K users will not experience any problems. Apple is aware of the problem and is working on a solution in a future OS upgrade.