Or cowl full of leaves and crap and it's overflowing the vent inlet.
There are small (1 inch holes between the cowl and the fender by the hood hinges that might be plugged up enough to cause that.
My car had a ton of crap down in the cowl so I ran water into it right down the intake vent in front of the windshield and used a section of wire to help things come out.
On the passenger side my car has a not hooked up vacuum tube controled smog part that had a fair sized hole under it so I got a wire in that way and rinsed with water also.