Firstly have to same I'm in love with libreelec.
Installed it on a Chromebox and its running perfectly.
I am using a little sound brick via headphone line out of the chromebox running into the line in on the sound brick which I switch on beforehand, and when Libreelec boots / shuts down, there is a loud popping / click noise before the kodi loads, and also when it all shuts off.
Is there any way to remove the noise, aside from turning the sound brick on after kodi has loaded?