Is there any plugin that lowers the sound volume of turrets? Couldn't find that option in turret plugins yet.

That's difficult since the sound is played client-side based on whether the client sees the turret as on or turning. The following plugin can fake turrets as being "off" which does reduce the sound and also disables the red/green laser, though there are still some sounds as the turret rotates. It's all or nothing, as there's no way to just disable the sounds.

https://umod.org/plugins/always-lootable-turrets

WhiteThunder

That's difficult since the sound is played client-side based on whether the client sees the turret as on or turning. The following plugin can fake turrets as being "off" which does reduce the sound and also disables the red/green laser, though there are still some sounds as the turret rotates. It's all or nothing, as there's no way to just disable the sounds.

https://umod.org/plugins/always-lootable-turrets

Just tested it and it works great, a new permission for the long time players to gain,
*one tip, you have to switch  off   existing  turrets and switch back on for the lights to go out  :)