i will be listening to music and, for some unknown reason, its onely comming out of the left speaker. i go to system pref and the knob/slider is all the way over. sometimes its onely a little over. it doesnt happen during play. just sometime between when im listening to itunes/movies,ect. totaly random. its been happing for as long as i can remember since ive had my tibook. anyone else have this prob?