Drive Side Wheel Question
 

My 2009 CE 320 Diesel have a kind of brown dust over the wheel rim in the driver side. The passenger side has a very small dust of the same color.
Just to make sure that i was not from accumulated from road I washed it very well and dried the wheels and drove the car as normally I do.
After a week driving the car I again noticed the same dust more in the driver side than in the passenger side and almost nothing in the rear wheels.
The car has ABS system working very well. In your opinion, can this dust coming from brake pads? If so, why I can hear no noise from squealing pads or any message in the car instrument cluster?
Can you help me on that ?
Thanks

Boringly normal.