Mildew Smell Coming From Car's Front Grill?

I own a 2003 Ford Thunderbird. For several months I have noticed a strong mildew smell coming from the vents, especially when air inside is on. However, I even noticed the odor in the garage when car was sitting in there. I started smelling all around my car and noticed the odor was very strong in the front right grill.

I thought I found the solution/problem when someone told me to change the air cabin filter. I changed it, but am still smelling mildew, coming from front right grill. I have sprayed bleach water solution in the grill, on the cloth hood cover, and in vents to no avail. Please help. Thanks.

By Cindy