I don't observe any specific pattern of this behaviour. Strangely, sometimes when my macbook reboots/boots, it plays a chime sound. And often in other cases, no chime sound is played. So what ...
Possible Duplicate: How do I disable or get rid of the startup sound my Mac makes? I have an old MacBook Pro (pre-unibody) running OS 10.6. I am annoyed by the traditional Macintosh bootup ...