Wow, that is a wasp's nest.
What does the exhaust pipe and intake grill look like? .... Pic?
I've had to modify my exhaust pipe in order to get it to install properly. The exhaust pipe outlet now has screen in it just for that same reason. I'm going to install screen in the combustion air intake as well when I reinstall the furnace.
I had a long conversation with Atwood this morning regarding my issues. They've gone ahead and authorized me to return the entire unit for inspection/analysis so I'll keep you posted as to the out come.