When I manually put the system to sleep from the main Application Launcher menu, even if there is no audio playing, it systematically causes a very loud click (or rather "pop" or "thud") on the audio line output, which is connected to external speakers. Even with a volume setting that is not very high, the click is *very* loud. Not only this is annoying, it can also theoretically damage speakers. And I'm pretty sure it's avoidable.

I'm not sure whether it happens 100% of the time. Actually, when I abandon my computer and leave it unattended (which is what I do when I stop using it), after a while the screen turns off and when I come back and shake the mouse it asks for password. I always assumed it was going to sleep, but I wonder if, in that case, it's just turning off the screen and locking with password without going to sleep. If it made such a loud noise in that situation, I would almost certainly noticed it at least some of the times (because even if I leave the room, I'm often not that far away).

I think it makes the same noise when shutting down or rebooting (obviously I mean from software; I do expect it to happen if I force-power down from hardware without shutting down nicely)

I hadn't noticed this until now, but manually sleeping, shutting down and rebooting are also things that I do very very rarely.