Ok, it is about 99% guaranteed that it is an internal short in the audio unit and you will either need to send it out for repair or replace it.
All you can do yourself is verify that there are no wires shorting against each other at the connectors. You will need to remove the center finish panel(see attached) and then you can unbolt and remove the audio unit and check the wiring and repair if any are shorting against each other(wires will be bare or cut). If ok as I suspect, then the audio unit will need to be either sent out for repair or replaced
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