Your audible tone could be a hardware fault, but is most likely a ground loop. Disconnect as many cables as you can and see if it makes a difference. If it does, reconnect cablkes one at a time until it comes back. Then you will know.
Your backlight issue again could be a hadrware fault, but also could be a setting. Try re-initializing the Eve/Net console (see UM).
Also, be warned that people often sell units with problems (sorry) rather than fixing them. You might want to contact the vendor.