What can cause the radio volume not to work on a 2004 Porsche Cayenne?

All radio functions work but there is no noise coming out of speakers. I already checked the mute button. Volume knob is operational but no sound.|||1.) operator error


2.) bad fuse


3.) bad button/knob


4,) blown operational amp inside radio


5.) speekers missing


6.) operators' hearing aid requires service/ or requires a hearing aid|||Volume control is a variable resistor electronic component called pots.Have your Porsche dealer checked it for you , it should be still under warranty.