Muting system volume upon logout using launch agent
In Terminal, execute the following command to disable the chime completely until reenabled:

sudo nvram SystemAudioVolume=%80

If this setting is not retained, try:

sudo nvram SystemAudioVolume=%01

sudo nvram SystemAudioVolume=%00

or

sudo nvram SystemAudioVolume="  "

To reenable the chime:

sudo nvram -d SystemAudioVolume

Info gleaned from:

https://business.tutsplus.com/tutorials/how-to-silence-the-startup-chime-on-a-mac--cms-21212

https://www.howtogeek.com/260693/how-to-disable-the-boot-sound-or-startup-chime-on-a-mac/