Ceiling duct work

[The Hawk]

Have noticed when I put the AC on that small flecks of a thin silver like metal come out of the ceiling vents. I think it must to from the flexable duck? Is anyone else having this occur?

[Gma-n-Gpa]

have not noticed any flecks coming out of the AC however, it has been more than a month since i last ran the AC (here in IOWA).