Chevrolet: 1999 Malibu Radio noise

Hello,
I have a nice factory am/fm/cd/cassette radio which has been awesome until
recently in which the AM stations are weak, lots of noise and just poor
quality reception. This does not appear to be an engine "whine" which
sometimes happens with an open ignition wire...The sound quality sounds like
searching for a station when in the mountains. The FM, cd player and the
cassette player all work great...
Any help is greatly appreciata\ed...
Happy Holidays...
Dennis