if the defrost tubes themselves smell mousey, replace them, you won't get rid of the smell otherwise, but most likely there's some nesting material in the heater box, your best bet is to take it all apart and give it a good clean out
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics
