Try this. Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the command(s) below:
sudo gedit /usr/share/polkit-1/actions/org.freedesktop.udisks2.policy
When it opens look for
<action id="org.freedesktop.udisks2.filesystem-unmount-others"> <defaults> <allow_any>auth_admin</allow_any> <allow_inactive>auth_admin</allow_inactive> <allow_active>auth_admin_keep</allow_active> </defaults>
And change it to
<action id="org.freedesktop.udisks2.filesystem-unmount-others"> <defaults> <allow_any>yes</allow_any> <allow_inactive>yes</allow_inactive> <allow_active>yes</allow_active> </defaults>
http://askubuntu.com/questions/552503/stop-asking-for-authentication-to-mount-usb-stick