Usually when I run my MBP off it's battery I mute my sound as i'm normally out in public if it's not running off A/C. Whenever I go to start it up again the startup chime does not sound (understandable as it's already muted), however, every subsuquent time I go to start it up, the chime still does not sound, even after i've unmuted the volume prior to shutdown. The only way to cure this is to reset the PRAM. This happens every time I shutdown on mute while running the battery power. Does anything like this happen to anyone else?