Is it just me or... When I have headphones plugged in, and my Macbook's volume is too loud / too quiet, when I try to adjust the volume it won't let me! Even if I only have like, 3 bars of volume on (out of the bunch that come up when you press the adjustment buttons)... when I try to make it louder it shows that all the boxes are full and there's a little "no smoking sign"-type-thing underneath the picture of the little audio waves. Has this happened to anyone else? By the way if I unplug my headphones I can adjust the volume again but it just seems weird. PS - Also, if I try to use a headphone splitter with two sets of headphones plugged in, the same thing happens. Isn't there supposed to be two headphone jacks on a Macbook because only one of them works for me?