We just bought a used 2008 KSDP. If there was any dust in the air-conditioning ducts, it's long gone now.
However, the previous owner warned me that I'd need to replace the passenger cab audio speaker as it sounded awful. He said it was blown.
When I removed the last screw holding the speaker up, I was doused with sawdust! Brand new, very clean sawdust. At least a cup fell out. I reached my fingers around the top of the hole and scooped out nearly another cup!
The driver's side speaker had less, but still a lot.
I posted this observation here and was informed that it doesn't happen often, but every now and then the Newmar clean-up crew messes up. The last thing that's supposed to happen on the assembly line is a complete vacuuming and cleaning.
Another possibility with your coach is that a ventilation duct might have partially detatched. Or, you've got mice up there! That's no joke. Mice have chewed a couple of holes in the furnace ducts in the basement of our 5th Wheel trailer. They use them as raceways to get from one end of the coach to the other. Before one gets caught in a trap, our cats chase them from floor furnace duct to floor furnace duct following their sound in the ducts. The cats think this is great entertainment. Grrrrr.
Woody & Sandy
2003 Chinook Cascade
2008 Newmar Kountry Star 3623