I have unibody 2.53 MBP hooked up to external speakers, via the headphone jack. When there is no sound, and the computer is ready to make a sound (mail alert, or start a song in iTunes, for example), I get a "pop" through my speakers. This didn't happen with my previous generation MBP. I suppose it could be the speakers or the connection, but I'm doubting it. They're pretty decent speakers (Klipsch). I'd also find it incredibly coincidental that something would go wrong with the speakers at the exact time I unplugged them from the old computer, and plugged them into the new one. Anyone else experiencing this? Any other thoughts?