I was surprised that my mom's '97 didn't have a cabin filter, no smell issues though.

With the hood up, try looking into the vent on the outside of the car where it draws in air, on that car it would be on the driver's side I believe.
Good chance of leaves, etc. getting in there which can cause odors when damp. Possible that some have made their way down into the fan enclosure in/under the dash as well if you don't see anything outside.