I have a CDM-9821 head unit, a 4 channel Alpine amp and a Alpine 6 disk CD changer. I hooked all of this up without mounting anything to make sure it all worked as expected. Everything worked fine. After mounting everything, the CD drive in the head unit and the changer both accept a disk, show time on tracks ticking away, change tracks, change CDs, accept and eject CDs, but there is no sound from the head unit when I use either the CD drive in the head unit or the changer. The radio works fine so I know it is not an amp problem. I have tried resetting the head unit with the reset button a few times to no avail. To the best of my knowledge, the AUX is off (the words AUX and off show together on the display). The manual states that if a changer is being used that the AUX has to be configured as off.

Does anyone have an idea why there is no volume from either CD player? I could understand one or the other not working, but for both to go out at the same time is just too weird. Yes, the CDs are inserted label-side-up, so I am not inserting them upside-down. One other thing ... there are no error codes.