[s-cars] Test signal from radio but not really

[Ira Deere]

'93 S4
Stock radio along with the rest of the stock sound
system.

When I turn the radio on I get this loud piercing
noise almost like a test signal, it is not adjustable
via the volume, however if you increase the volume
knob position you can hear the music playing.  Test
signal occurs in any mode.  Seems to be coming from
the left rear speaker but I'm not 100%.  Any ideas?
How can I replace the stock radio with an after-market
and still use the factory CD changer.  Thank you in
advance
Ira

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