My friend needs help on his MacBook Pro-This is what he said: "I was messing around with garageband with speakers on, and then mixing and messing around with tracks when suddenly there is this popping(?) noise and then the sound goes out. Doesn't reappear until I restarted it. What's happening? I tried putting it to sleep but then when I unsleeped it again the popping noise appeared..." ... This happened to me too. Mine just went away with the sleep though. (I gave him the advice to do that.) Please post back, thanks.