hi everyone. i think my mpb has two problems with the audio system. the first one is a low volume / high pitch hiss coming from the right speaker which starts immediately when a sound is about to play (from itunes songs to the quack you hear when you change the volume). when the sound stops the hiss lasts for around 25 seconds, then stops. is very low but such high pitched that it gives me almost an immediate headache. changing or muting the volume doesn't change the hiss, while it stops when i plug some jack into the headphones port. i read many posts related to this hiss thing, but they seemed to regard the cpu or the fans. this is triggered by a sound event, and this is why i think its something in the audio system. the second problem happens when i use skype. i didn't change anything but since yesterday i can't hear the other's voice, not even the skype test call voice. Of course the audio is working, and from the speakers i can perfectly hear the ringing tone, but not the voice. If i plug in earphones i can hear both the ringing tone and the voice. it's not normal, is it? i called apple care and explained the thing, they told me to bring the mbp to assistance. since i'd prefer to solve the problem as soon as possible i tried to format and reinstall everything sadly, nothing changed i don't know what to do.. is there a mixer app or something where things might be messed up? thank you..