powerman — It sounds to me more likely that the problem is with the DSP (Digital Signal Processing) / power-amplifier unit that sits on the floor under the passenger's seat. It is responsible for controlling the volume, tone, muting, etc., and for amplifying the signals for each the eight loudspeakers (it contains eight channels of power amplification). It receives its audio and control signals from the radio unit. I suggest that you have the dealer try plugging and unplugging the three connectors at the amplifier, and making sure that the grounding bolts are tight. If this doesn't cure the problem, maybe the DSP/amplifier unit is defective.

Stan