I think these two might be related.
From searching here:
It looks to me like mice can enter the heater area and get to the recirc plenum, but not in the heater box since the fan has grilles
I think my heater cover will help keep them out although they have yet to try
Mice get behind the dash, which is pretty hard to do from inside the car, but the chassis is open at the back and they can walk right up to the front behind the dash and wreak their tiny havoc. They did get in there a little prior to my ownership, leaving some gnaw marks on the foam under the sill panels and a little pile of paper towel bits forward of the gauges
So this is where the exhaust smell comes in, I put some sloppy foam in the back ends of the chassis last year, and it seemed to subjectively make it better, but not perfect, basically if you are driving and roll the windows up you get a burst of exhaust smell, and occasionally at random times.
thinks he solved it and I was ready to make up the blocks of foam, loaded the pic into cad and measured them even, but I took the pic below and it looks like the factory did at least some sealing of the sills.
So I am thinking of squirting a little spray foam around the edges of the pictured block[it is a pic holding my phone in the sill pointing back]
also the gap shown in the second pic opens straight to the sill, rearward of the foam block i think so I will seal that up
For the mice I bought some fine epoxy coated hardware cloth that should look fairly neat installed at the back of the chassis openings and maybe some closed cell foam there also
Can you tell I live in the woods?