Musty smell

I’m always cleaning out the dust bin, and I wash and rinse it and let it dry. I clean out the inside where the dust bin goes. I’ve cleaned the brushes. I’ve even attempted to wash the HEPA filter (it’s not old enough to replace IMHO), but I still have a musty smell coming out of the unit whenever it runs. I have small dogs that shed, so that is why I clean the bin so often. I’ve had numerous Roombas in the past, and I never had this issue with them.