CGT, mice in the ductwork--alternate air intake location?

[Jonathan Monetti]

I live in NW New Jersey where, after the first frost, the field mice heavily
arm themselves, build small siege towers, and attack all winter long.  They
are often pretty successful.   They have an affinity for my Coupe's duct
system (strangely, they don't bother with any other part of the car).  

Last year I saw that the little monsters chewed a small hole in the plastic
mesh covering the opening to the air intake duct, under the cowl's rain
shield.  After I cleaned out the system I replaced the plastic with a heavy
aluminum mesh. 

Somehow, someway, they get back in. 

Barring some random place they may have chewed through (a defensive breach,
so to speak), I can't figure out where they are getting back in there.  I
know mice can squeeze through some very tiny holes, but the aluminum mesh is
a fine gauge.  

So...is there another, less visible entry point into the air duct system I
don't know about?  

TIA,

Jonathan Monetti
'02 A4q 1.8t
'87.5 Coupe GT