Your Sonicare toothbrush measures brushing motion so it can tell if you start scrubbing, which can be harmful for your teeth and gums. If you regularly scrub while brushing, the app will recommend that you enable the feature.
Once activated, the feedback light at the base of the handle will show amber, and the toothbrush will vibrate differently. The light and vibration will return to normal when you stop scrubbing.
Note: your toothbrush does not have this automatically feature activated. To enable it, see "How do I turn the Scrubbing Feedback feature on and off?" within the FAQ.