Little tiny brown specks, why?

you should be using greasless on a sprail and with wheels i polish them then clear them it saves work on the long run

[Gerarddm]

Polishing a set of Cromodora Daytona alloy wheels. Sandblasted off the old finish ( BTW, NEVER do this! What a pain getting the surface back down...), then used 240 greaseless/sisal, then 400 greaseless sisal to get the finish where I could use an emery wheel, then hand wet sand with 600, 800, then DuPont polishing compound by hand, then Simichrome final polish by hand. Put a wheel away in its cardboard box in my cold garage and came back to it in a week or two and it has tiny brown specks that are corrosion? or something, because polish didn't work and I had to go back to 400 wet sand, then back down the sequence to Simichrome to get the specks out. What is causing this? Any prevention possible?