Cadillac 2007 CTS Owner's Manual page 374

Brake Wear
Your vehicle has four-wheel disc brakes.
Disc brake pads have built-in wear indicators that
make a high-pitched warning sound when the
brake pads are worn and new pads are needed.
The sound may come and go or be heard all
the time your vehicle is moving, except when you
are pushing on the brake pedal firmly.
CAUTION:
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The brake wear warning sound means that
soon your brakes will not work well. That
could lead to an accident. When you hear
the brake wear warning sound, have your
vehicle serviced.
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Notice: Continuing to drive with worn-out
brake pads could result in costly brake repair.
Some driving conditions or climates may cause
a brake squeal when the brakes are first applied or
lightly applied. This does not mean something is
wrong with your brakes.
Properly torqued wheel nuts are necessary to help
prevent brake pulsation. When tires are rotated,
inspect brake pads for wear and evenly tighten
wheel nuts in the proper sequence to GM torque
specifications.
Brake linings should always be replaced as
complete axle sets.