OEM Radio (electrical problem)

[autos]

    I'm having an odd problem with my OEM Nissan radio. This is the
original AM/FM/Cassette, I believe it's called the 2200 model, in a 1993
Sentra SE-R. It's in new condition and very well taken care of.

    The problem is, when I listen to the radio, all the radio stations
sound over modulated. I live well within the class A signal for all the
stations I tuned to so it's not the station signals themselves. Also,
when I play a cassette in the unit or CD on the OEM CD player, it sounds
fine, so it cannot be the OEM speakers. It just sounds like the antenna
is receiving too much signal.

    Any help/thoughts are appreciated,
                            Eric Hope