Optical output - how to disable

I wonder if there any way to disable the optical output on WD TV Live. I got two WD TV boxes and both of them leave the optical output on even if the WD TV is off. Optical output always lights red and warming up the WD TV box. So, is there any way to disable it? I can accept it should go on and work if I switch WD TV on, but when it is off what is the reason to leave the optical output on?

Other than switching the WD off at power source, go into audio setup and select stereo.

Thanks for advice, but it is already set to stereo and the optical output still lighted red.

How about a putting a piece of tape over the port?