Problem solved! When I removed my radio I took it apart to see if I could get at the volume control to replace it. I removed the faceplate and discovered it had special screws which I had no way to remove. I put it back together and ordered new radio. Today I hooked up the original radio to see if it made any difference for the tone. The tone disappeared "and" there is no more problem with the volume control. Something must be interdependent with the radio removed to cause the tone. So I re-installed the radio and all is good "for now!" Thanks everyone for you help and suggestions.

Well it's solved but I don't know why it's solved.