In Garageband '09, while scrubbing through 1 track I encountered some performance lag issues, which I clicked continue. But then all sound basically has given out and I hear pops instead. Even other apps such as iTunes and Quicktimes all I hear are pops. I quit the applications and reopen but same result. Only fix I found was to reset my system. Checked my System Preferences>Sound>Output>Internal Speakers (Type: Built-in Output). Not sure what is happening. Any help much appreciated!

Macbook Pro 2.8ghz Unibody
Mac OS 10.5.8
Garageband v5.1 (398)