Do you know what this is?

Hi

I am trying to get the television / dvd working on the SAT NAV screen. When I click on the TV button on the SAT NAV screen all I get is a Black screen and a loud whistling noise? I had a dig around in the boot and found a little black box on top of the GPS Navigation System unit. I followed the wire and it ended in the boot. It was unplugged but in the general vicinity of the TV tuner unit? Does anyone have any ideas as to what the little black box is and what it does?

I understand from reading posts on here that you cannot watch TV on the SAT NAV screen as it is an analogue signal and you require a digital tuner? is this correct?

Should I still be able to watch DVD's on the SAT NAV screen? do you put the DVD's into the GPS Navigation System unit? I would have expected it to say "DVD" somewhere?

thanks for your help

Tony