I also wanted to get rid of the sound because I have my computer boot up every morning before I wake up so I can use it as an alarm clock. I have to have the volume set loud so the music will wake me up, but this means the bootup sound wakes me up first. I live in a dorm, so I don't want to disturb my roommate with it too.
I was searching this just now, and another thread gave the name of a program, Mac Pilot, that allows you to change a lot of default preferences you normally wouldn't be able to. There is a setting for muting the startup sound in Mac Pilot. I have yet to restart my computer since changing it, but hopefully that will work. The only problem is that it's only a 15 day trial, so once that's up, I'm stuck with whichever preference I set.
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Fear is a waste of time, and pain breeds fear -- ignore pain and live life.