RV Repair: foam from ceiling vents, ceiling vents, natural breakdown

Question
I have a 1997 Cruise Master and the foam in the ceiling is falling out without running the air or heat. It is like a snow storm when the air is on.It is coming out of the ceiling vents.

Answer
From the sounds of it, and not being able to inspect it myself, it may be mice. They might be getting in and building nests that eventually make it up and through the vents. Another cause would be natural breakdown of the insluation and it's finding it's way through the ducts. Without specifics on the type of insluation and type of Duct work, that's where I'd start.....