Time to revive this hilarious thread
So, this is indeed RV related (well, this happened in a van stored in a hangar that sometimes houses my RV...).
I have a old Ford conversion van, which I keep in a small tin hangar near where we have a summer getaway camper parked about an hour or so NW of the Twin Cities by RV. We stopped to get it on Friday, and upon starting it, I heard what was clearly something being ground on by the heater fan. This was followed about a half second later by a distinct stench, like that of a mouse nest. Nice. The grinding stopped fairly quickly. When my wife stepped into the van, I got a dirty look as though I was the source of this stench. Not this time, I said. As we drove on, I wasn't sure either of us could keep our lunch down. I turned the heater to off, and we drove with the windows open. We got to our place, and I opened the hood. More stench. I pulled the motor and fan assembly, something fairly easy to do. Whoah, there was a big glob of mouse nest in the plenum, and about 7 or 8 juvenile mice.
Now, there is a fair amount of good luck that came my way during the 10 minute drive. With the heater set to off, the damper door separating this glob of mice from the cabin was opened. I.e., the mice were probably watching my wife (if one had jumped out on her, there would have been an ambulance involved). Anyway, back to this family of mice - I ran into the garage to see if I had anything that could knock them out - starting fluid! Perfect - it is ether, which was used to knock people out in the olden days. I sprayed a bunch right into the nest, rendering the invaders quite silly. (I was imagining how to tell my insurance company that the car torched when I was spraying starting fluid into the heater system...) I cleaned the mess out, and hopefully the stink will subside after I fogged the duct system with Febreze.
Oh, yeah, one of the mice had more than a bit of his hide missing - must have been the grinding sound.
I do not know how they navigated into the plenum - there might have been a boot loose (this boot feeds cooling air to the fan motor).
On a serious side - mice and other critters can be very dangerous to our planes...