https://askubuntu.com/questions/191527/disable-auto-opening-nautilus-window-after-auto-mount
The simplest option is to open a terminal with Ctrl+Alt+T, and type:
gsettings set org.gnome.desktop.media-handling automount-open false
or
Turns out, it is. You will need dconf-editor tool, which can be installed by with sudo apt-get install dconf-tools. Run dconf-editor in your terminal. Browse to org -> gnome -> desktop - media-handling Uncheck automount-open.
