just did an oil change/filter look-see. The cabin filter was solid full of acorns.

Actually it is mice that have deposited those items in your HVAC system! .. It’s a very common occurrence that we see quite often at the shop.. You have a good idea but the screening material will need to be a bit more rigid than the ordinary screen door variety Turn key on and blower on high - listen on passenger side with hood raised and you should be able to locate the fresh air inlet from the roaring sound. Good luck with the mice!

Thanks for the quick response Pushrod. I sure do hope the whole situation was from the previous owner. The car is low mileage and spotless (well, it was until now). Again, there are no oak trees near me at work or at home so I will keep my fingers crossed and follow your good advice. I think I will also pull that new cabin filter and the blower motor out and blow it all out with compressed air. Again thank you for the (horrifying) info… p.s. NO mice allowed here.