Perhaps you guys can shed some light on a problem I've been having with my internal mic in my MacBook 13". I record a lot on Garageband and often switch back and forth between using the internal one and plugging in an external one. Now I'm not sure if switching drivers frequently is the cause of this, but lately I've been noticing a loud hissing sound when I record using the built-in mic. Anyone have any experience with this or any ideas about what it could be? Much appreciated.