GMC Yukon Denalid Owner's Manual page 337

AM
The range for most AM stations is greater than for
FM, especially at night. The longer range can
cause station frequencies to interfere with each
other. For better radio reception, most AM
radio stations will boost the power levels during
the day, and then reduce these levels during
the night. Static can also occur when things like
storms and power lines interfere with radio
reception. When this happens, try reducing the
treble on your radio.
FM Stereo
FM stereo will give the best sound, but FM signals
will reach only about 10 to 40 miles (16 to 65 km).
Tall buildings or hills can interfere with FM
signals, causing the sound to fade in and out.
XM™ Satellite Radio Service
XM™ Satellite Radio Service gives digital radio
reception from coast-to-coast in the 48 contiguous
United States, and in Canada. Just as with FM,
tall buildings or hills can interfere with satellite
radio signals, causing the sound to fade in and out.
In addition, traveling or standing under heavy
foliage, bridges, garages, or tunnels may cause
loss of the XM™ signal for a period of time.
The radio may display NO XM SIGNAL to indicate
interference.
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