I recently moved into a 100 year old home that was renovated in 2000. Every so often, I will find white powdery dust on a a counter or on the side of a wall. It almost looks like drywall dust, but all the walls are painted so I don't know how that could be. We live a block from a train track and sometimes at night I can feel the house shake slightly, so I am wondering if that might be causing the dust to accumulate? I am pretty sure there is no more plaster left in the house, but maybe I'm wrong. Any ideas what it could be??