Hide Mounted Drives

Open a new Terminal window (Ctrl + Alt + t) and run this command: $ gsettings set org.gnome.shell.extensions.dash-to-dock show-mounts false

The change will take effect instantly and mounted drives showing on the Ubuntu Dock will instantly disappear from view.

If you change your mind and want to re-enable mounted drives on the Ubuntu Dock in future, just rerun the same command, omitting the ‘false’ switch at the end like so:

$ gsettings set org.gnome.shell.extensions.dash-to-dock show-mounts true

You can access the same setting via a GUI if you install the dconf-editor tool and navigate to the org > gnome shell > extensions > dash-to-dock page, switching the show-mounts toggle to the off position.