Just to give you guys a heads up on this issue. What you are experiencing is commonly referred to as "rail dust" but would technically fall under the umbrella term "industrial fallout". The little rust specks you are seeing are tiny pieces of ferrous particles that have landed on the paint, bonded to it and started to rust. Most likely the cause of the fallout you are experiencing is from your metallic brake pads. The dust comes off and is very hot and the particles will actually embed in the paint. Clay WILL NOT remove the particles. Clay will knock the exposed portions of the fallout off so it appears that the problem is fixed but if the particle has embedded in the paint it will continue to rust and will be visible again quickly. The only way to properly fix the problem is through a specialized 3 step wash system that will 1. neutralize the acids in the paint from acid rain 2. dissolve and remove the ferrous particles 3. bring the paint back to neutral ph and follow up with a coat of wax or paint sealant.
It's a pain in the *** and depending on the amount your brakes are shedding dust it can happen quite quickly. The best way to prevent it is to wash the paint 1-2 times per week.