I sit with my 08' alum-ubody 13'' macbook on my lap very often. when I maneuver myself into a new position, my macbook always maneuver with me. but i've been hearing a unique sound that it makes if I tilt it too steeply. this sound closely resembles the same sound a flourecent light makes when it turns on. --ting!-- just a few decibels louder than a pindrop. any idea what this is?