Oh yeah, they do that when the pads are getting down close to the sensors. It will go on like that in the rain for awhile. Then you will start to get a solid indication when you step on the brake hard. Then you will get some flashing going along, and an indication every time you step on the brakes.
Then it will stop. At that point the wear indicators are gone.
You get lots of warning of pad wear. Really a great system - it allows you to plan a long time in advance for pad replacement.