Ford 1996 Crown Victoria Manual page 186

When the radio waves are reflected off objects or
structures, the reflected signal cancels the normal
signal, causing the antenna to pick up noise and
distortion. Cancellation effects are most
prominent in metropolitan areas, but also can
become quite severe in hilly terrain and
depressed roadways.
To minimize these conditions, a stereo/mono
blend circuit has been incorporated into this
system. This feature automatically switches a
weak stereo signal to a clearer monaural signal,
which improves the quality of reception.
Several sources of static are normal conditions
on AM frequencies. These can be caused by
power lines, electric fences, traffic lights and
thunderstorms.
Another reception phenomenon is Strong Signal
Capture and Overload. This can occur when
listening to a weak station and when passing
another broadcast tower. The close station may
capture the more distant station, although the
displayed frequency does not change. While
passing the tower, the station may switch back
and forth a few times before returning to the
original station.
When several broadcast towers are present
(common in metropolitan areas) several stations
may overload the receiver, resulting in
considerable station changing, mixing and
distortion.
Automatic gain control circuitry for both AM
and FM bands has been incorporated into this
system to reduce strong signal capture and
overload.
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