Musty Acura MDX

Hi-I posted this in General Discussion, but probably should have been posted here.

Briefly-I have an '04 acura mdx, and upon starting the car with the AC on a musty-mildewy smell comes from the ac vents (never did this until recently).

Changed the cabin AC filter and sprayed with lysol disinfectant-good for 2 days, but smell is now back.

Drain hose is draining.

Any thoughts?