Subaru Forester EyeSight 2015 Owner's Manual page 91

Troubleshooting
A noise occurs when automatic braking control activates.
This is the sound of the automatic braking control operating.
Braking control activates frequently when driving in heavy traffic.
Unlike a human driving, the EyeSight system performs control based only on the
actions of vehicles or objects in front. As a result, acceleration and deceleration
may be more frequent. If it is difficult to maintain a consistent following distance,
do not use Adaptive Cruise Control.
A small jolt occurs when cruise control is used on a downhill grade.
Downshift control occasionally occurs on downhill grades, and may produce a
small jolt if it activates.
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