On the way back from AITP today I stopped at services, and when I came back to the car the CD player refused to output any sound. Its a 2007 A4 Cabriolet, non-bose with the Audi Navigation 5.0 Headunit. The volume control does nothing, and turning all the way down does not enable the mute symbol on the HU. Pressing the power button activates the mute symbol but unmuting it gives no sound. Balance is set all the way to the right Fader set all the way to the back Trebel & Bass both set to full. I searched on ASN and no results. Googled it and a few people suggested wiring harness wearing out i the door boots, but that wouldn't explain why the EQ & fader/balance settings changed themselves. Tried ejecting CD, changing CD, switching from CD to radio etc, turning off and on again, ignition off and on again, all to no avail. I'm going to try it again in 30 mins or so and see if it's some kind of software glitch in the HU, but has anyone else experienced this before? Is it the sign that the HU is on the way out?? TIA for any help!