Could you have tried something such as a "log-out hook" as described in Mac OSX Hints?
This uses modified script to select Mute just prior to logout, and also shows some of how.
• Mute the startup sound using logout hook: (from 2003 to 2009)
http://hints.macworld.com/article.php?story=20031005165919533
The last note at the above page shows how one person ran a logout hook.
Mute the startup sound using a logout hook
Authored by: koit on Jun 14, '09 10:47:41AM
If you'd done that, maybe the suggested paths could help find such a device?
Also other ideas, *using code to silence startup chime on Intel-based Macs*:
http://hints.macworld.com/article.php?story=20070223093835709
Some of the other forum hints go on with
more interesting stuff in their comments.
A general search using terms, as follows, may bring in methods; one
you may have utilized to disable the chime, and then maybe reverse it:
*Mac OS X 10.5: disable startup tone in Terminal*
+Hopefully someone with greater insight and short post answers will reply with an+
+idea of how to search for or reset just the default volume on startup in your Mac.+
+Short of an "archive & install/update" regimen. Or restore from backup clone, etc.+
(Oh, we're heading into sub-zero °F temps again, here; not including a chill factor.)
Good luck & happy computing! 🙂
PS: In the Universal system preference panel, there is an option in Hearing to make
the screen blink instead of hearing Alert sounds. I wonder if that carries over on restart
and stops the startup tone? ...I don't use Universal Access preferences.
+{ edited 2x}+