We had this same problem with our natural eared dobermans. The long ears prevent good air flow to the ear and can allow bacteria or yeasts to grow in the moist environment of the inside of the ear.
You should see a vet on this one. They’ll give you a tube of ointment that will kill the bacteria and/or yeast that is causing the problem. You put a few drops in the ear, massage it in, and repeat everyday for a week or 2.
They also might recommend regular ear cleanings at home, using a product that is made just for that. It is a more watery substance, whereas the ointment is rather like vaseline in consistancy.
Good luck!