well, it's just happened about two days ago when I used battery. then now it's also happened both of using battery, and plug-in. when macbook starts, bip noise for 1-2 seconds. but it's gone after that. I have no idea why. it didn't occur before. does anyone know or the same experiene before, or now? I also posted the same question on apple discussion. but nobody answered. help me. of course, I went to apple store for asking why. but genius didn't really know what's symptoms was. the guy was not genius, but retarded. anyway, I'm waiting for answer as quickly as possible. thank you.